There's no other way other than to simply keep trying.
Frequently however, interviewees are curious to know the reasons why they didn't get the position, especially if it was a position they really wanted or needed.
Here's why it's so hard to get those answers.
If nothing else, knowing exactly why you didn't get a particular job from the interviewer could be very valuable in finding out the mistakes you made so as not to repeat them in the next job interview.
If you try to find out however, more often than not you'll simply get industry wide standard responses which tell you nothing.
Such responses include "We didn't feel you were right for the job" or "We went with someone with more experience".
The problem is that in today's culture of suing and lawsuits companies are somewhat paranoid about exposing themselves to any hint of possible discrimination.
Telling you the real reasons why you weren't accepted for the job could expose them to that risk.
It may also be a case of just not caring and they could feel that it's wasted time to find out from the interviewer why you weren't awarded the position.
They just have too many other 'more important' things to get on with.
It's also true that managers don't want or like to give bad feedback to interview candidates, I guess no one likes does really.
In the case of a larger company it may simply be a lack of communication or knowledge on the part of the person you're talking to.
The actual interviewer may have no information from the HR hiring manager as to why you were refused the job.
In all cases accept the disappointment and move on, it's not enough just to try, you have to keep on trying.