Comment by ltbarcly3

I would just say "why can't you just use xxx". If they are moderately competent, they will instantly say "xxx doesn't work for this because the abc can't be compiled on this hardware", they'll have thought of it too, because it's probably not just obvious for you, and now they have helped you get up to speed on this complex problem.

I don't think you can use magic phrases, or avoid magic phrases, to manipulate people into feeling one way or another about you. You aren't insulting them by asking obvious questions, you need to hear the answer. If it took them 2 weeks to get stuck and ask for help, it's going to take you at least a few days to figure out why this is actually a harder problem than it seems. Avoiding the 'obvious question' because you think your colleague is too fragile to answer it and think nothing more of it is far more condescending.

What if they didn't think of it? Either they are very inexperienced, so they shouldn't be insulted by an expert providing expertise, or they are experienced and will slap themselves on the head and laugh about it, or they are an intolerable jerk, and who cares what jerks think of you?