Today I wasted about 6 hours trying to understand a proof about how the interior of a set is always open because I couldn't put the pieces together that if the points of the open ball around a point were all members of the interior then the open ball was a member of the interior.

I don´t know what the fuck was I thinking, maybe something along the lines of thinking about the ball as a bag and the points as its insides rather than piecing together that the insides were in fact the ball.

This all has left me feeling like a fucking disappointment, should I go back to the basics and just read a book on set theory? We just skimmed through the definitions at the start of undergrad and it had never been a problem until now.