I have seen many managers make trouble for themselves by treating their team members' estimates as commitments. An estimate is not a commitment, and the difference between the two is significant for managers.
The essence of an estimate is expectation. When you give an estimate, you express your expectations about what will happen. Built into each estimate is an element of uncertainty. If you weren't uncertain, you would use a word other than "estimate."
The essence of a commitment is promise. A commitment is a pledge or promise. When you make a commitment, you declare your intention to create some result, and you invite someone (usually another person, but sometimes yourself) to rely on your intention.
Though commitments always include an element of uncertainty, uncertainty is not a defining element of commitment. Though estimates often include an element of intention, intention is not a defining element of estimates. Estimates are about expectation. Commitments are about intention.
Suppose team member Fred is writing the installation guide for your product. You ask Fred, "What is your estimate for when the installation guide will be ready to go to press?" Fred says, "Two weeks from today."
If you were to take Fred's estimate as a commitment, you would create trouble for yourself. How does this create trouble? Two ways. First, it gives you the possibly false impression that Fred intends to deliver the installation guide two weeks from today. Fred may indeed intend to deliver at that time, but he may not. He may be expressing not his intention, but only his best guess.
Second, treating Fred's estimate as a commitment downplays the uncertainty inherent in his answer. Is Fred highly confident that he will deliver in two weeks? Moderately confident? Barely confident? It's hard to tell.
If you were to make commitments of your own based on Fred's answer, you would be promising results that Fred himself has not promised (in his mind), and that Fred may not be confident of delivering. That's a risky basis on which to make promises.
When Fred says, "Two weeks from today," is he making a promise, or merely stating his expectations? How confident is he in the date? Answer those questions before you make your own commitments based on Fred's estimates, and before you ask Fred to "meet his commitment."
Estimates are not commitments. If you want commitments, don't ask for estimates. Ask for commitments
Experiment: To determine whether your team members see their estimates as commitments, try this test. The next ten times you ask for estimates, ask also for commitments. How close are the estimates to the commitments?
Experiment: If you think I'm all wet, and you're sure that when your team members' give estimates they really are making commitments, try this test. Stop asking for estimates, and from now on ask only for commitments. If you balk at that, perhaps you see estimates and commitments as not quite the same.
Experiment: If you ask Fred, "When will you be done?" have you asked for an estimate or a commitment? What does Fred think you asked for? If Fred says, "Two weeks from today," has he given an estimate or a commitment? What might happen if you want a commitment and Fred thinks you want an estimate? What might happen if you want an estimate and Fred thinks you want a commitment? How could you make it crystal clear whether you're asking for an estimate or for a commitment? How could you make it crystal clear whether Fred is giving an estimate or a commitment?