How to deal with frustration?

Hey guys, im really frustrated and dont know what to do. I like the game and i want to become better but some characters frustate me really hard. Ken, cammy, Kimberly and now mai is really unfun to play against. Most of the time im in the corner and getting a throwloop/mixup. I watch guides and lab them a bit but i just cant beat them. Their mental stack is just to high for me. How do i get better against mixup/rushdown characters?