people

People will do things just because they are people.
Economics does assume that people will be rational, well for that matter I presume ever so often just that - that people are rational, but people sometime just do things that seem to contort logic.

Probably because there is more emotion in there than anything else.

And that is the blind spot that sometimes makes us do things.
Not in any way bad or evil, but just because the logic of the situation does not stare us in the face.

And though we do things fallaciously we never expect others to be just like us.
We generally expect them to behave rationally.

And that is what makes people difficult to understand.
We expect people to behave accordingly based on the imperatives of intellectual logic.

Ah, c'est la vie.