Why is software estimation often referred to as an art?

The work programmers do is complex, and often there are various unknowns. Therefore, a programmer needs creativity to convince the business that it will not take a long time to complete their tasks.

The work programmers do is complex, and often there are various unknowns. Therefore, a programmer needs to take multiple factors into account when providing an estimate.

The work programmers do is complex, and often there are various unknowns. Therefore, a programmer needs to add extra time to every estimate they provide.