Being someone who keeps their word can have value, but sometimes it doesn't. If someone kidnaps you and then forces you to promise to give them all your money when they release you, it's bad. If they knew you wouldn't keep your word, they wouldn't have kidnapped you. That's why contracts made under duress aren't binding. I don't think duress is the only reason to break a promise. Another one is that you were stupid. You don't want to make promises you'll later regret, so if someone doesn't accept your promise because they predict you'll come to regret it, that's good.
The kidnapper should precommit to kidnap a fixed number of people regardless of their propensity to keep to contracts made under duress. Like many precommitments, this harms the kidnapper if he actually has to follow through with it under unfavorable circumstances (he may know that nobody keeps such contracts, in which case he's precommitted to kidnapping people for no profit at all). However, it reduces the measure of worlds with such unfavorable characteristics, thus financially benefitting the kidnapper on average--if you know the kidnapper has made this precommitment, you can no longer use the reasoning you just use above and so you will obey contracts made under duress.
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.