Trump has a thin skin.   Just be grateful that he does.   This is why he has to remind everyone he played the election game fair and square and the attempts to change the rules at the end by some is like awarding the world series based on number of runs scored instead of games won.  

That thin skin and fear of failure is what is left to keep him rational and less impulsive.

As many have pointed out, he had good strategy, and instincts and he probably got very lucky to tap into the global wave of anti-elite anti-globalist sentiment in a a way that Romney could not (or the timing was premature in 2012).   

His strength is  having to fight the establishment of both parties, soros, koch, wall street, media, hollywood, DC think tanks and bureaucrats, he does not owe any established faction anything --- other than the small number of loyal supporters.

His weakness is that he has no legislative or governmental experience, and he needs to recognize that.  He appears to have done so.