I think I finally got it. I have been rolling the word around in my head for quite some time. Over a year now.
It sounds counter intuitive, but I've found the essence of commitment to beinsensitivity. When you are more committed to something there is less that will change the situation. That is to say you are now less sensitive to the things that would have changed your situation before.
I know we are supposed to get this warm idea when we think of commitment but I'm most of us know the ugly side too. The ugly side is that commitments make us insensitive, or perhaps better put insensitivities make us committed.
I like to put commitment in to real terms, rather than idealistic terms, which is why I try to think of the insensitivity causing commitment. You can try to shape your sensitivities so as to create a certain kind of commitment, but that commitment is not realized until the sensitivities have been changed, muted.
In this sense commitment is not merely a choice, or no more than putting on your pants. It requires action. But also commitment does not necessarily require a choice. Through happenstance your (in)sensitivities may commit you one way or another without volition, just as you may find yourself wearing pants without your choosing.
We don't usually think of engineering commitments. Or at least not our own. But it is certainly a possibility. I suppose we usually put more emphasis on engineering our sensitivities, even if we don't call it that. In this frame we would be more likely to call them 'interests'. The reason we typically don't talk about engineering our own commitments is the same reason we don't encourage insensitivities... insensitivities create missed opportunities. Commitment is about not investigating or pursuing certain classes of opportunities. This is counter to our interests. Though it is certainly in my interest to have people believe I am no longer pursuing certain classes of opportunities.
Once others believe I am not pursuing such opportunities like, alternatives to a partner, my partner is more likely to stop pursuing alternatives to me. When this happens I will be more comfortable with a break in partnership than will the partner, so my partner will make larger compromises to maintain the partnership. This is profitable though results in often highly asymmetrical relationships.
It takes resources to maintain sensitivities. That is why it is often so tempting to commit. Committing frees up the resources that were being used to look for alternatives.
Mutual commitment allows both parties to free resources they would otherwise have been using to look for alternatives, yet the balance of compromise is maintained as when they both had full knowledge of alternatives.