What is your biggest stressor

I realized a few days ago that one of the things that stress me out the most is when I realize that I have given someone my word and the situation changes such that my commitment is now likely to take a hit.

In purely transactional cases, such as a software deliverable that is clearly going to miss the deadline, the right thing to do is to apprise the client of the new situation so that he or she can inform ahead and avoid bigger problems for all. That is exactly what we do. It is better to take the bitter pill now than to have to address a ton of bitterness later.

The tricky part is when you see that there is a chance that your commitment might fall flat, but there is also a chance that things might work out.

What should one do in this case? The simple act of informing the other party does not necessarily suffice. If you have always played it safe and informed the other party, only to be okay most of the time, then the other party soon learns to disregard your warnings. Alternately, if you do not inform the other party until the situation becomes obvious, they would be right to be upset that you did not inform them earlier.

The situation gets even trickier when we are dealing with our personal lives, where the commitment is more than transactional.
Let us say you have promised yourself that you will do such and such for your children's future. But as life is wont to do, there will be some surprises and let us say you find that commitment slipping. This kind of stress is more long term, the kind that clogs arteries and puts you on the track to an angioplasty.

Is there a way to alleviate this kind of stress?