Because whoever you think you are, you’re probably right. You will continually take actions based on who you think you are; it’s your identity.
On the other hand, others think something about you. The actions you take will be filtered through how they see the world.
Best case scenario is that how you perceive yourself and how others perceive you is in sync.
On the other hand, you could just choose a path and stop worrying what others think about you.
Just a thought.