Okay, after, like... ten minutes of trial and error, I finally get it. All horizontally aligned sections are considered "targets", which can also be "trapped" areas. Nothing in the game tells you this (I see ten individual segments, so it's natural to think a "trap" would have to be in only one of those ten segments, not a given horizontal row), and it's entirely luck-based if you draw the exact cards you need.
I've also had several rounds now where I wasn't drawing any "candle" cards and had three 1-target "rope" cards... so I threw away the one that I thought it was least likely to be. And wouldn't you know it, the next candle card I drew said I THREW AWAY THE WRONG CARD ON A 1/3 CHANCE, and the only other cards that could hit the same spot would also hit a ward. If that happens, congratulations; you're irrevocably fucked.
If there's one two things I've learned playing this game: 1) 3-target "rope" cards are almost always useless; and 2) there is never a reason to discard "candles". (There's a third thing, but I'm keeping that a secret. Y'all will probably discover it by accident anyway.)