I once spilled lactic acid because I just assumed it flowed as fast as water. It would have been a simple mistake, but I specifically obtained that bottle from my twin sister who had prepared a similar mounting medium with it AND warned me to use it sparingly because buying it takes half a workday, ..., and I had listened and promised to be careful. I could have her show me how to do it, but she was time-pressed and irritable because her supervisor demanded she present her thesis before the institute (something like a preliminary hearing). Looking back now, I realize that asking her help then would have only taken five minutes, and there were literally no people who would be more willing and able to go out of their ways to do it.

I think asking yourself 'does it really cost so much to approach this person for advice?' is a good heuristic to have.