The two are very much related.  Doing what you say you will do is probably one of the most crucial factors in  building trust.  An acquaintance has the opposite habit of committing to something, and then either not follow through, or cancel at the last minute.  I know people aren’t perfect, and don’t pass judgment based on an incidence.  But after a pattern developed, I knew that I couldn’t trust that person anymore. 

Sometimes people agree to commitments simply to avoid a conflict.  But eventually but following through, they destroy their own credibility.  So it’s better to say no upfront, and set the proper expectation.  It requires a bit of courage, but at least trust and reputation won’t be shattered down the road.