'Gain' in the Bible

What does a person gain in all his toil with which he toils under the sun?

What does the worker gain in his toil?

This also [is] a grievous illness. Exactly as he came, so he will go. What profit [does] he gain for all his toil for the wind?

So do the wise [really] have an advantage over fools? {Can the poor [really] gain anything by knowing how to act in front of others}?

Blessed are you, O land, when your king is a son of nobility and your princes feast at the proper time-- to gain strength and not to get drunk.