from my experience even two people who can work together well and form a duo is a rarity
and even then it's usually  the multi-talented  ones ( graphics and game design + programmer duo seems to be most commonly successful)
as a rule of thumb the bigger the team the bigger the chaos - there needs to be at least one persistent and headstrong fellow to hold things together (who is not necessarily the leader)

in the end I find that some projects beyond a point simply 'complete themselves'  and most of the work is spent on 'finding the end of the tape' and the real benefit of a team comes when you finally see clearly what the finished project should look like and there is a lot of grunt work needed to get there 🤔

never trust anyone with your code

I've worked in a team once here for a jam and other times with friends for some other jams. Everything went well, because we stated what we expected from each other from the beginning. But I know not everyone is so reliable over here.

I work also with a team in my job. We knew each other because we studied together but we weren't friends (at first, now it's another story). Our team suffered a lot of changes. Some people were dissapointing and some people gave more than everyone expected. Fact is, we didn't hesitated to left outside the team anyone who were not involved enough in the work or the people who keep on missing deadlines without a proper reason. You have to be able to say "you are out of the team" without regret if things go wrong. It sounds awful and it's not fun, but sometimes things are like that

And, important advice. Make all of the team members sign a NDA contract, even if just one person, or even if there is not finacial benefitc from the game. Just, do it, it's very important because if things go really wrong, you can take legal actions.
There's A LOT of other factors to take into account about team work, but I'll stop with the rambling

Sooner or later I will have to cooperate with one or more people for a project, it's something common in this, isn't it?

No.

But if you can't program, you have the short end of the stick. It is easier to comission assets or find free ones.

There is a reason  why most games use an existing engine and basically design their "level" on that engine. That is not only a lot easier, it saves on need for programming knowledge. You only need to learn how to operate the engine for the basic stuff. For story telling that is only superficial programming. Implementing actual logic, even something like creating a tetris clone, that would be lot's more demanding on programmin skills.

To elaborate my no,  most games I saw on itch are single person made. If I see groups, it is basically a small company already. 

Trabajé en un equipo de 4 (hacía diseño de niveles y personajes) recuerdo que se trataba de algo llamado "Backrooms", recuerdo que era un laberinto 2d y pixelart, había una persona que hacía el código a veces lo hacía en su casa, privado, yo y el resto del equipo llegamos a su casa y vimos lo que estaba haciendo, había convertido el juego en un juego de 18+, terminamos expulsándolo del grupo, fue horrible, aquí son algunos dibujos que hice para el juego:

I will answer you with my experience, and what other have told me and what I have seen. Also I know what it's like to work with people you see everyday and people you simply met on the internet.

First I will answer to "It's something common isn't it ?" Well, yes and no. It's more common than what I might believe (I can think of already a few people who made a game by themself), but no it isn't as common as to say that no one has never once work with someone else, see what I mean ? It's not common for someone to not have at least one experience of working with someone even if it's just hobby, but there's tend to be a lot more people doing their own thing alone those past years with how it is easy to learn Game development in general (by this I mean, it's easy to learn information freely or not through internet).
However, you are limited as to what you can do and how much time you can do it. To do something all alone means you have to learn everything (and believe me, when you think you know something you have only scratched the surface), that everything need to work well together, and how long it will take to create that everything will depend on three things : "how long does it takes you to learn this" , "how much time can/will you give it" "how many mistakes will you do before being able to realise what you want" . And of course, you will be limited to your knowledge. In overall, you can work alone if you wish to, and I think it's a good thing to be interested in everything little by little, but don't try to do grand thing at first and simply find your flow.  Anyway, back to the topic.

How was it in overall ? Well, going to be honest, not that good, but not that terrible either. I found out that there's some people that are rare pearl, that know how to do everything, other that are learning but have their heart to the right place with a burning desire of learning everything they can, while other are simply incomptent and sometimes terrible people to other.
My words may seem harsh when I say some people are incompetent, but honestly some truly are; I don't mean specifically their skill; some of them are self taught some are not who cares, but they refuse to listen to other; or are egocentric and everything they do tend to not work or simply are not good idea (or it's not pleasant to work with them). Some people simply aren't made to be in video game, or to be in your group because they don't fit or else. I've had a really bad project because I had also people I could not count on, of course I did mistakes but not being able to trust each other because of this or that well the worst mistake without a doubt, it wasn't a pretty sight at the end.
I would say, you want a good team ? Have an excellent communication. Even if your vibe or else do not fit with them, it doesn't matter, communicate well as long as you share the same point of view for your project and are respectful and listen to each other it should go well, honestly you need to be able to trust your team or duo, if however you know after some time that you can't count on them well, you either disband the team or duo or if you have no choice you try to find way to work with them. Depend of the project, if it's pro or not and how many people are here, but if you are not a lead you can't fire someone, and to fire someone there's need to be proof and complain anyway let's go back to internet.

On internet, people sometimes will ghost you that it's intentional or not it will happens so honestly considering you don't know that person, don't know their skill, don't know how to judge their skill, don't know w h a t their skill are or who they are it's honestly a big fifty-fifty. I do think that if you make a post about wanting to work for a team and people answer you on that post, it means they want to so if something goes wrong it might be that their skill either are not that good or it's not nice to work with them; even if someone is kind, if they don't listen to you or worse if you don't share the same view of what something could be, you're in for a ride. On this, it's good to have clashing idea, it's not good if that clashing idea is the opposite of what you see for the game; especially if it's the beginning (pre-preeeeee production) or if you are only two. 

To have a good note, because it feels like there had been only negativity in my post, it's not that there's only negativity in working with people but most people simply see the good and not really the bad, because honestly the good is what you expect, there's good people working in video game, passionate be it in real life, on the internet, as a hobby or as a professional, you'll meet a lot of people that share the same passion as you and many are lending each other their hand; it's honestly a wonderful thing to be apart of, a wonderful thing to see. You might connect with people, less with other but still work and admire what they do; it's a never ending cycle.

I've spoken a lot about the human side of a team, on the techincal side let me tell you it will be a mess. Communication is the key, but sometimes when you don't know how something work there will be a mistake. Working as a duo is well, fine on the technical part; you are only two and if you have connected well it will be fun. Now working in a team as many as 8, when you take back what I said about everyone skill there is some thing that don't work. The skill are too different, or simply people who have never worked with each other need to adapte. It's a mess when it's a programmer with a programmer, there's a reason why a programmer should never go into another programmer's code AND a reason why in video game an important part of our job is also tied to having good documentation so that the communication works. On the artist side, it's the version of "a programmer in a programmer's code", people will have to work with your work so any mistake will fall on you without.... good communciation (Take a shot each time I say communication). But in overall it's a big mess as at the beginning because it's the unknown and everyone need to adapt and see who is "good" who is "not". The most difficult part has always been communication between programmers and artist, because when you create a video game there's soooo many parameters you need to know that are more than simply doing 3D, or doing concept or doing code (I could go for hours about this), that simply are technical. It's good to know how things work on each side.

I wanted to finish by saying that when you are many on a team, you need a lead, someone who will have the final decision. A good lead isn't someone who give order and bark at you, it's someone who also care for the project and know how to get things done (which mean understanding how each people are and work to know what can be done or can't). A good lead is, I don't know, honestly an envoy from god because they can carry the team, the moral and have the competence to do so. A bad lead will simply make things go sour faster.

I will be honest when saying sometimes things don't work and it's for the best; just as sometimes things work and it's for the best. I don't want to paint a grim picture of working with a team because it's not; but I thought I should focus those point because as I said earlier, the good is exactly what you think it is, the bad you may not know until you experience it. I simply want to be as honest as possible. It's a messy thing, that sometimes is disastrous but also an amazing and fun experience that will teach you so many things no matter the outcome and will let you meet amazing people !


(I apologize for the long message !)