While this is a key to philosophy, it is also a key to one's personal psychology. Without correcting this view of oneself, one cannot be happy. (See the definition of what comprises happiness: Happiness) People waste so much energy on having a dysfunctional view and set of beliefs about themselves. If one focuses on getting realistic views and beliefs about oneself (and mankind), then one will save a huge amount of resistance and effort fighting (false) barriers. Also, one will not put artificial limits on oneself by a false view of oneself.
This is vital, critical, essential to living a good life. It should command your time until it is fully and effectively designed and owned.
Some of the highly erroneous beliefs that people have are discussed in the following pieces:
Who I Am - Without this understanding, you'll spend time on useless defending or self criticism. Knowing that "I" is not what you think is vital to self understanding. I Am Powerless - A belief that people develop, but with no truth to it. See why.
I Am Not Good Enough...Not! - This is a very correctable stance - and it must be corrected if one is to be happy. It's not optional. It is always fixable, though.
Practices and viewpoints that affect one's view of oneself