"Whether you think you can or you think you can't - you're right"
This is Henry Ford, one of the hundred people who changed the world. I like him personally - with an exception for how he treated his son, but that's another story.
Why don't people believe they can do things? I've watched for the pattern in people around me, and it's always the same one: they believe being great is something you're born with. I've caught myself believing it too.
But when I look at my own achievements, honestly, none of them came from talent, luck, or timing. They came from consistent practice. I think everybody would find the same if they looked. Everyone is great at something, and that something is always the thing they practiced a lot - not the thing they were born gifted at. Talent does matter, but here's how I see it: being born with talent means being born with a good engine. A good engine helps you move faster. It doesn't drive anywhere on its own.
So the first step to believing you can do anything is breaking the belief that greatness is innate. Belief can be trained. But - and this is the part people miss - it has to be trained logically. If something realistically takes a week, don't lie to yourself that you'll finish it in a day. That's a fake belief, and fake beliefs are harmful: when you inevitably fail, you won't blame the ridiculous deadline. You'll start doubting your belief, your strength, your ability, everything. Instead, set a milestone you can actually hit, hit it, and let the win strengthen your belief. Then set the next one. Belief is a muscle, and this is how you train it without tearing it.
When you find something you're afraid to master, look back at what you've already achieved and how. It was practice, every time. So go do the thing. You can.
Someday I'll be thankful to myself for writing this down now.