When your boss asks when you’ll have that project done, how do you come up with an answer?
I like to under-promise and over-deliver.
If I estimate that I can get the project done by Tuesday, I might reply that I’ll probably finish it by Thursday or Friday.
Under-promising and over-delivering is a good tactic to keep your boss (or client) happy because most people are loss-averse. That means that they dislike losing something of a certain value more than they like gaining something of equivalent value.
Concretely: your boss would feel the sting of you being two days late more than she would feel the pleasantness of you finishing two days early.
Under-promising is not being dishonest. It just keeps both parties happier. And who doesn’t like it when someone over-delivers?