Cui bono

From Liberpédia
If you ever wonder why people around you are behaving strangely, or believing and doing seemingly irrational things, you can find the answer by asking the question: what’s in it for them? It’s remarkable the extent to which people craft their own opinions and decisions around their own desires and interests, regardless of considerations of truth, evidence, or logic.
Jeffrey Tucker, Adults-Only Observations: Five Bad Things and Five Good Things about Life