My friend is going through a career change right now and it's been a painful process: for every interview where they end up saying "no", she feels like it is a personal rejection.
I'm here to remind you that sometimes, the task at hand is really not a good fit.
Consider all the times you have said "no" to someone else (telemarketing, anyone?). Consider all the times when you wish you said "no" because it would have freed you up from a time-sucking or non-productive event. Consider saying "no" when you really don't see the presented opportunity matching your personal life mission.
Then understand that other people are going to say no to you, too. This means that your "YES" answer will be perfectly suited to you. In fact, the more you hear "no", the closer you will be to reaching your perfect, fabulous "YES" answer.
Get used to hearing "NO" as an answer. That means you are out there, you are trying, you are seeking, and you are gaining experience and wisdom to understand when the YES appears.
I've heard this from sales people and from personal development people alike. When you have more clarity about your "NO" and "Absolutely Not" lists, you will get closer and closer to the people, places, and situations on your "YES" and "Absolutely Must Have" list.
The more you say NO, the greater it frees you up to say "YES" and really mean it.
It's nothing personal. It's nothing related to you as a human being. It is not a reflection on your character. It's just not a good fit at this time.