Casters. Everyone plays them, but the question is; who's actually fit to play the role? When do you know when to move on from this, or keep playing it to further your playstyle? I've played almost every role.
Sit down kids, prepare for a history lesson.
*Clears throat, leaning back in rocking chair*

I started this game in June of 2010 under the reccomendation of my old World of Warcraft guild, Brute Force (Twisting Nether realm). My first game was with Blitzcrank, and I started with Exhaust+Heal, and I took my E as my first ability. I went to Wolf Camp after not buying any items, and I died. I proceeded to call the game a piece of ****, and left. A few days later I picked it back up again, and needless to say I was still terrible. I was building 6 Stingers on Rammus, and 6 Heart of Golds on Taric. I was ****ing atrocious.
I still had no idea what I wanted to play for a role, until Xin Zhao came out. Yes, he was brokenly overpowered upon release, and I loved this. I played him and constantly got into 1v3's and came out with a triple, then proceeded to get a pentakill off the remaining two. I felt unstoppable. I thought I had finally found my role on League of Legends; how wrong I was. After Xin received a few nerfs, I picked up Evelynn. Every game I played, I went 20-4-15 and other extremely positive similar scores. I was in love with hybrid Evelynn with a heavy side of AP.
Somebody told me Evelynn was banned in ranked, so I stopped playing her. At this point, I still had no idea what I wanted to do. I decided to pick up another champion: LeBlanc. I was on fire with her, unstoppable for the longest time. Eventually I got bored of her playstyle, so I switched over to an AD. I discovered Corki and Kog'Maw, and I fell in love all over again. It was an arduous road, full of failure for about 20 games; but eventually I learned them. I told everyone that Kog'Maw and Corki were most likely the best characters for their archetype, and everyone called me ******ed; proceeding to bandwagon and say "ASHE OP!!!11". Disappointed, I stopped playing them because of the amount of hatred I would get for picking them. Even late game when I completely dominated, people said I could have done better with Ashe. I still felt like I wasn't satisfied with what I was doing at this point. I just hit level 30, and I had no idea what I was good at. I was mediocre at best with every role, spare a few champions. After some more trial-and-error with dozens of other characters, I fell into a niche with Vladimir. I had played him briefly at level 24 or so, but I never really caught onto him. I played him for hundreds of games, perfecting every single possible thing you could do with him. I had found my role: I was best suited for an AP caster. With my newfound character and role, I felt on top of the world.

What's the point of all of this banter, you may ask?
You always keep learning with League of Legends. Since the time I started, I've discovered many champions including Cassiopeia, Vladimir, Anivia, Jax, Kog'Maw, Malzahaar, and Sion; to only mention a few.

Your knowledge will always be cumulative, and always listen to peoples advice. It may take a few hundred games before you realize it, but eventually you too will find your role.