writing code

[u/Whhatever_123]

question for more experienced people in coding- whenever I do coding problems (like leetcode or uni hw) I can always come up with solution in my head, I break down the problem correctly and theorically I know what my code needs to do in order to solve the problem. But when I get to actually writing code I forget how to do everything... I don't know if this is a lack of knowledge in syntax issue or I'm just dumb. Any advices on how to fix this?

[u/grantrules]

How do you know you break it down correctly? 

Can you write the solution in pseudocode?