Would you live with a stranger for so long without knowing anything about them?
It is very important to know yourself for at least three reasons:
First, you have to live with yourself 24/7. Essentially, it is about self-awareness, which leads to greater personal understanding. No one in your life will be with you as much as you are with yourself. Who you are, what you like and want, where you are going, what makes you happy, and what makes you irritated: those are very important things to know if you are to improve the quality of your life, and take advantage of the things that make you glow.
Second, self-awareness builds confidence. The more you know about you, the more secure you will feel emotionally, and the more adept you will become at dealing with situations. You gradually become more intuitive about what works for you, and what doesn't. Self-awareness is a powerful tool for improving competence, because you will be pushed along directions that make you feel good, rather than living in a vague way from day to day, not knowing how you feel, or what you should be doing.
Finally, self-awareness boosts identity. If you don't know much about your background, history, culture, gender and what you value, how will you get on with others in mutual respect? They cannot respect what they don't understand. People who lack self-awareness tend to be ambiguous, often making others feel uncomfortable, because they are never sure what to do, or what they want. So ignorance about the self is not a good thing. Self-awareness builds self-esteem through personal appreciation, understanding, and acceptance.
Knowledge is power, but the greatest power is self-knowledge.
If you do not really know much about you, how can you appreciate yourself, or others? Most important, how can they value and appreciate you too?