In "If" what does "If you can bear to hear the truth you've spoken" mean?
As always with any question that asks for the specific meaning of a particular part of a text, it is vitally important that you read the quote in context. This means that you pay particular attention to what comes both before and after it to make sure that you are able to understand the quote in its entirety and the point that the speaker wishes to make. This quote therefore comes from the second stanza of this thought-provoking poem:
If you can dream - and not make dreams your master;
If you can think - and not make thoughts your aim;
If you can meet with Triumph and Disaster
And treat those two impostors just the same;
If you can bear to hear the truth you've spoken
Twisted by knaves to make a trap for fools,
Or watch the things you gave your life to, broken,
And stoop and build 'em up with worn-out tools:
This is of course when the speaker continues his list of things that you need to be able to do to be considered a "man." In particular, we can see that from the line that follows the quote that you are asking about, that one of these traits and abilities is to be able to hear the "truth you've spoken" repeated back to you but "twisted by knaves to make a trap for fools." The answer to your question therefore is based on the way that we can often speak truths but our words can be twisted and manipulated to obscure that truth and made into a "trap for fools," which is obviously something that is very distant from our original intention and purpose for speaking. Maintaining our integrity and clinging on to the truth of our original words in the face of such manipulation is something that proves us to be a mature individual.
When you've been kicked down, get back up and do not by any means allow that kick to destroy your true self. Become stronger and wiser because of those lessons learned. Gather all things that are broken in your life and put them back together again to make it stronger. Strength is in the way you handle the stressful times in your life whether those stressors are good or bad