If you don't challenge yourself from time to time, how will you know what you are capable of?
How will you grow?
How will you improve?
How will you find out what you are really made of?
Yes, sometimes challenges are difficult. Downright hard. But that doesn't mean they aren't doable.
Sometimes you fail. And sometimes you succeed. In the end, neither really matters.
What truly matters is that you got in the arena and gave it a try. Gave it your all. You stopped letting your fears hold you back, and you did something. That's what counts.