A banker opts for short-term gain despite indications that his decision might not pay off in the long run. Which error or bias is the banker guilty of?

The banker is guilty of bias or error called Immediate Gratification

Explanation:

Immediate Gratification is a term that describes the urge or want of individual to get result instantly without delay. In other words, it is the propensity to seek for immediate but little gains or profits, as against delayed gratification which can yield better or more gains or profit.

In this case, the banker, wants short term gain, because he seeks for immediate gratification, despite indication showing that such decision might not pay off.