You may have heard the cliché before: What holds people back is not who they are, it's who they think they are not. Even I, having heard this and read it many times, can utilize the mentality check that comes from reading this statement.
What are you not doing right now that you want to be doing? Why aren't you doing it? Usually it all comes back to that principle: something we feel like we are not. Nothing more than that stands in the way.

You're not approaching that girl because you feel you're not the type she'd go for.
You're not starting that business because you feel you're not quite ready to be an entrepreneur.
You don't score more points in the games because you have decided that you're not the type of player who can do it
All of the above have the same conclusion: if you believed you were, you'd be doing it!
What's stopping you, right now, from changing your mind?