WaiterRant has an extraordinary post. Read it to renew your faith in people.
It is interesting how so often we remember the small gestures over the large ones. Children recall something you said that you don't even recall. Co-workers mention something you did that boosted their careers and you draw a blank.
We encounter people every day who carry burdens that we don't even suspect. Being kind and respectful is the least we can do.
Who knows? They may remember it 30 years from now.