1. What is it?
The ego is an idea of yourself rooted on the opinion of others. It is an identity that serves as a preliminary answer to the question: "Who am I?".
A lot of vital aspects of your life derive from this identity such as your purpose, goals, and dreams. Pretty much the reasons to wake up every morning. When your ego is questioned and jeopardized, the aforementioned aspects are also shaken, and it feels awful.
To cope with this condition people constantly look for ways to reinforce their ego, to confirm their identity, and this process is called validation.