I apologize in advance if this question is too discussion-based, however, I do ask purely to get an answer/suggestion, and the site did prompt "Ask about... Understanding mathematical concepts and theorems."
So it's not that I struggle immensely with combinatorics but it seems like a branch of maths that either you're good at or you're not good at, and there's no way to improve unless you learn to think in a specific way. There's this concept of "combinatorial thinking" that I'm struggling to grasp. Basically, how can you ensure that you have considered all the cases? And there aren't really any "silly mistakes" you can make because it's just that you are thinking/interpreting the question incorrectly.
I could just do a bunch of problems but the problem with that is I usually attempt around 5 questions and then when I look at the solutions they are all wrong. For other topics, a question I get wrong might be because of careless algebra or reading the question incorrectly. Are there any excellent resources for learning combinatorics to a high level out there? I want to be someone who can solve "all" (most) combinatorics questions, and someone who people come to asking for help with combinatorics/probability questions.
For the problems you do know how to solve, or for textbook examples, one method is to try to find a second way to solve to the problem. You can almost always do this in combinatorics and probability. This way, you know what you are trying to aim for and you are forcing yourself to learn many different techniques for these types of problems.
As you do more exercises you can continue to do this and you should hopefully see your confidence towards this topic building, as long as you also pay attention to your mistakes and trace your steps to see where you went wrong and adjust accordingly.