How Do You Guys Learn New Champions?

So I have a curse. I can't learn new champions anymore. Seriously. I've tried. I am a decent , a play-making WHO DOESN'T EVEN BUILD DAMAGE TO BE A MAJOR THREAT, and a scary fucking . But for some reason....for some motherfucking reason every time I try to learn someone new no matter how many times I try and no matter how calm I be and how many losses my teams have to suffer so I can try someone new, I can't learn anyone else. SIMPLE CHAMPIONS SUCH AS I can't play to save my life, because I do absolutely horrible game....after game....after game...ect. ect.. And cause my unfortunate team to lose game after game after every fucking game I play them in. I can be on a HORRIBLE loss streak and get told to kill myself 50 times in one night and still keep calm, but the second I pick up someone different and new it's the hardest and most frustrating fucking experience I've ever had in League. YES. This is a rage thread. I'm flat out pissed at myself because I can't even get the basics down for Yi...FUCKING YI but I can set up pentakills like it's nothing as J4 or Amumu or Anivia or some shit like that. So I ask: how the fuck do some of you guys manage to learn new champions? Because repeated failure with no improvement no matter what I do is not helping me at all.