There might come a time when things in your life are going especially well. You have worked hard and there are good results. This is not the time to think that you have arrived. In reality, there might have a been a bit of luck involved (which is nothing to be ashamed of). The circumstances can change soon enough. This is especially true if you take your eye off of the ball.
This is true in the corporate world, this is true if you are running your own business, it is true if you are a performer (such as an athelete); it is true most everywhere. Younger people are maybe more susceptible to believing that they have arrived. So watch for it, and catch it in the bud.
On the other hand, one shouldn’t obsess over it. Just keep your eyes open and don’t necessarily believe it when people tell you how wonderful you are.