Here is how I have rectified this for myself (though I am not the hardcore developed of some on HN, I've hacked a lot of stuff together for fun and profit).
Developers rarely know what users really want in advance. Hell, even users don't know what users really want. Re-writes are time consuming (and, to me, boring), it is easier to do the minimal amount of work first, demo that, take feedback, and then build it out.
However, going into this you need to have faith in yourself that you can deliver something good, and on time. If you have that confidence in yourself that you can deliver the functionality expected in a reasonable time frame, you can possibly be more comfortable selling ahead of your delivery schedule.
Developers rarely know what users really want in advance. Hell, even users don't know what users really want. Re-writes are time consuming (and, to me, boring), it is easier to do the minimal amount of work first, demo that, take feedback, and then build it out.
However, going into this you need to have faith in yourself that you can deliver something good, and on time. If you have that confidence in yourself that you can deliver the functionality expected in a reasonable time frame, you can possibly be more comfortable selling ahead of your delivery schedule.