Five simple words. Three if you don't count the hyphens: Under-Promise And Over-Deliver.

But time and time again, what do we do? Over-Promise And Under-Deliver. Which one makes our boss and clients happy?

Why do we do this? Why do we constantly over-promise what we can do, bunch up our priorities, and then disappoint when we deliver late? And why do we do this again, and again, and again?

Here is a scenario to stop this dysfunctional cycle:

It's Monday. You are given a project/task to do. Your boss or client asks when you can deliver it.
You know in your heart, you can easily complete it by Wednesday. And if you work extra-special hard, Tuesday night.
So you say, "I'll have it to you Tuesday night. WRONG! This is where the train derails.
You should say, "I'll have it to you Friday. Is that okay for you?"

Your boss or client will respond in one of three ways:

80% of the time - "That sounds fine. If you can get it earlier to me that would be great."
15% of the time - " Oh. Can you get it any earlier to me? Say Thursday?"
5% of the time - "That won't do. I need it by Wednesday. Can you do it?"

First, why do I have you buffer the time from Wednesday to Friday? Simply, because stuff happens. Unexpected calls, emergencies, breakdowns, other clients, other projects, home emergencies, etc. You get where I'm going.

Unfortunately, we don't plan for these things to happen. But they do - all the time. So you need to buffer. What happens in this scenario?

You deliver on Thursday (comfortably) instead of Friday and your boss/client thinks that you're a genius (and hard worker).
You deliver on Thursday (comfortably) and your boss/client thinks that you are a person of their word.
You tell you boss/client that Wednesday will be very tight and you might have to move around some projects/tasks. You deliver on Wednesday.

If you begin to do this with all of your projects/tasks, you will find that your time is better used AND your boss/clients will love you.