What are the most difficult aspects you find when learning English?

Hi everyone! 
My name is Ari and I'm currently working on my final dissertation. I'll focus it on the main difficulties we find when we are learning English and how to overcome them. So I'm very interested on what are the main features that you find particularly hard and what are the main mistakes you keep committing when you are writing or speaking. I'm refering to the grammar, listening comprehension, orally speaking, reading... any area! So please write from your own experience what you think and if you want to, you can write what are the easiest points that you've gone throuhg learning English. Thank you! 

Ari