ego.

I believe that people has a good heart in nature.
a heart that is able to think about others above ourselves.
a heart that is willing to help others to succeed.
a kind heart.

however, sometimes ego kicks in.
it closes our eyes to those good stuffs to reach our personal goal.
"I will do anything as long as I am happy.
as long as I am not hurt.
as long as I succeed."

ego makes us does not realize that we may be hurting others.
your ego might suffocate other persons that are close to you.