Example: I main Darius: the dude everyone hates fighting. Yeah. Raise your pitchforks, I deserve it.
Darius is very strong in dueling, with near unmatched duel sustain (only rivaled by perhaps illaoi), heavy burst, immense tankiness, movement crippling, godly duel potential, and 1v2 potential (or even 1v3+ if fed enough). As such, he does amazing against champion's whose weaknesses are Darius' strengths. For example, Darius tends to nut when fighting Naut top, as Naut lacks the burst or mobility needed to deal with Darius, and he just serves as a Noxian might meatshield for Darius.
However, he also has some really heavy weaknesses. No movement speed sterroid forces you to take ghost or build deadmans if you want more effective chasing, this movement speed weakness also means he's doomed if an adc knows how to kite (and he essentially can't kill ashe for this reason), if the enemy is super sticky, Darius loses all his sustain (so someone like riven or fiora), or someone who can displace/escape from Darius after he somehow gets on them (so someone like quinn, vayne, or zilean). As such, when I see zilean top (which I've actually fought a bit), I cry, as there is little to nothing I can do if the enemy is smart.
However, say I only fought matchups I was comfy with. Say I only fought Malphite, Naut, Yasuo, Garen, Aatrox, Mundo, and the such. I really wouldn't grow, now would I? I would only learn how to abuse Darius' strengths, and I would learn certain things, like animation canceling to get more passive stacks, flash Q to get noxian might, etc.
We all have those games where we fight hard champion counters. For me, it was stuff like vayne, ashe, quinn, graves, fiora, riven, Jax, Morde, and such. With some champions I fought, I learned that I shouldn't just blindly run into them. I really shouldn't blindly run forward into the enemy vayne, even if they're 1/5/2. I'll get chunked if they kite, and I will die. Rather, I learned after many bad games that the best course is to back up, hope vayne makes a mistake and tumbles into E range while chasing, then pull her in and commit. I learned that some champions actually outdamage me, even if I play to my strengths. Jax, fiora, and morde will dumpster me if I treat them like any normal fighter or juggernaut. I have to try and pick my fights, accept my loses occasionally, and look for windows to abuse. Stuff like that. Yes, theres a heavy chance I'll go 2/7 that game, and have my entire team flame me by saying something like "Wow who feeds with Darius? He's so broken, omg ur so bad". But I'll learn. I'll be tilted, but I'll learn.
Not really sure why I made this post. Just wanted player that were having bad games to hang in there. If I can climb from bronze 5 to Diamond 4, then by golly you can hit that skillshot.
(Also: mini Darius counterpick tip to those who struggle against him. Zilean with lethal tempo or glacial augment is Darius' biggest counter by far. Use this info as you will)