I love that quote by Muhammad Ali: "It isn't the mountains ahead to climb that wear you out; it's the pebble in your shoe." It reminds me of the fact that our biggest challenges are not the things that happen to us nor the paths we have to follow; the biggest challenges we'll face as humans are internal. Our attitude towards life and the big picture we see. Our lives cannot rise above the thoughts we have.
It is the limitations we set ourselves and not the difficulties that life places before us that determines the richness of our lives. It is what you go after that you get. You don't get what you don't go after, no matter how much you deserve it.
It is the pebble of the limiting beliefs you have about who you are and what you can become that determines how far you go in life. It is the man who believes in the perfect work of God, that God has given him potentials beyond what he can wrap his mind around, and goes all out to realise those potentials that go the farthest in life. He gets rid of the pebbles in his shoe and no matter the mountain, he can climb without undue pain and wounds. All he ever faces are exhaustion and minor setbacks that time can heal.
One way I use in getting rid of my limiting beliefs is to consider the entire universe and my place/time in it. It helps me to remember that I'm just a tiny blink: I am like an invisible dot around for less than a blink. And my problems are much tinier and short-lived. This knowledge helps me to lose all fear of failure and not feel too big about my successes. It frees me to stretch myself in all dimensions as interest me and to want to climb mountains rather than stick to my tiny corner.
For you, it might be a depressing way to view life and not a way to get rid of your own limiting beliefs. You have to find out what will work for you. You have to find out what will help you lose all your fears and do all the things you really want to do. You have to find out what will push you to take on the mountains that matter to you. And you have to find your own way of motivating yourself past the exhaustion and setbacks you'll face along the way.
Of mountains and pebbles, your bigger worry should be getting rid of the pebbles in your shoe and then climbing the mountain will be an achievable task.