Many times we doubt ourselves and don't
believe in ourselves. why do you think
this is so? what can you do to believe
in yourself?

A lot of it could be the way we were raised, or the environment we grew up in. Self - doubt usually first occurs when we fail at something, most of us don't get the realization that humans fail, we all are going to fall, or make mistakes, ...but practice makes purpose. We must keep trying, when we self loath, doubt and hate it can actually be the very thing blocking us from succeeding, not a lot of people have come to that realization. Wanna believe in yourself? learn to become more aware, self aware.