I'm as guilty of this as any other author, but my rule of thumb is... if the response to an input includes the EXACT words that a player may have tried then you have to program that input in if possible, otherwise they're going to feel annoyed/cheated. So as the response includes "You strike the flint and...", I think you have to include STRIKE FLINT... even if it's just a response that says "What do you want to light?" or "You create some sparks with the flint. Definitely enough to start a fire."... which lets them know they're proceeding along the right sort of lines.