It is never a good idea to assume superiority as a result of your accomplishments, regardless of how impressive they may look to the external world.
First and foremost, because nothing is permanent, and any accomplishment and the perks that come with it only describe a temporary situation someone happens to be in.
That is why it is a good idea to practice in our minds the genuine possibility that this might all go away. Because sooner or later it will. The Stoics call this art of negative thinking premeditatio Malorum, developing resilience through the mental exercise of visualizing things that can go wrong or be taken from us. As Seneca wrote, 'we should project our thoughts ahead of us at every turn and have in mind every possible eventuality instead of only the usual course of events.'
Secondly, because you actually "did not build that."
You might have surely worked very hard, have an excellent academic record and be blessed with an impressive IQ. So what? There are a lot of hard-working, smart, and very creative people in this competitive world with outstanding academic credentials too. We need to recognize that in all our accomplishments there is this element of serendipity, of being in the right place at the right moment that we can take very little credit of. We cannot deny luck playing a significant role in helping us achieve many of our goals.
Thirdly, because a healthy sense of humility will prepare yourself better to face any future setbacks and avoid to be crushed by any little failure.
This means not feeling self-important as a result of your successes, but humble and willing to pay them forward and helping others in need. Don't detach yourself from others but always remember how similar you are to them and how fickle fortune is. One day you might be trading places.
Lastly, because a self-aware leader is a humble one.
Humility is not a matter of low self-esteem and poor self-image. Humility is about recognizing the truth about oneself, and our accomplishments, which entails recognizing both our limitations and our gifts, our role in making things happen and the role chance played in our successes.
C.S. Lewis defined humility as not thinking less of yourself but thinking less about yourself. From time to time it is very comforting forgetting about ourselves and turning our attention outward to others, isn't it? And the more we acknowledge the fact that fortune is fickle, that our achievements are not only ours, and that we are not different from those that are today in need, the better leaders we will become.