a likely benefit triggers action

People and animals decide how to act based on a sophisticated and usually subconscious cost /benefit analysis they conduct.

People and animals have already run a cost/benefit analysis of each behavior they repeat, and know the benefit(s) repeating each of those actions will yield.

When a human or an animal foresees that it is very likely that a specific action will produce a specific benefit, he or she will execute it.

Thus, "a likely benefit triggers action."