Everyone's brain might be different, but that just means you might need different mental techniques then someone else. For example, I'm terrible at memorizing things, my working memory is rather small compared to the average person I've come to find[1]. To adapt, I focused on finding things that would let me compress memory, focusing on the 'core' of things so to speak and ignoring everything else. For example, in math and physics, I ignore pretty much all the equations and instead try to find the similarities that tie everything else together and use that to derive/figure out the rest as needed. This way I can get away with knowing much less. (I've also been lucky to have teachers that let us reference the equations on tests). Suprisingly, I found this acts as a great foundation for learning new things, letting them slot together much more readily. (I also got into the habit of using a notebook as both a reference and workspace for ideas, letting me refer back to things that dropped out of my working memory quickly)
The thing is though, if I didn't pressure myself to develop that habit in the first place, I would never have improved.
I think a huge part of mental ability is simply having motivation to go through the process.(admittedly a large part of motivation is biological/just how you are wired)
[1]This is a bit subjective, the important part I think though, was the pressure it caused me to put on myself to improve.