How good a book is is depends on how readers respond emotionally too it which means they first need to connect with your Main Character. This is why your MC needs flaws because no one can relate too someone who is perfect.
So what kind of flaw does your MC have? When does the flaw show itself?
Be specific about your flaw don’t just say something like “Is rude.”
When is your MC rude? To who is he rude? Is he outright rude or with simple small comments.
You have to be specific.
The problem is your readers should still end up cheering your MC on or they won’t read what you wrote. So the trick to the flaw is balancing out the severity of the flaw with how often it is triggered.