Playing ADC is suffering
Title. The entire enemy team wants to kill you, and specifically you. You are super important for the team to kill towers, and you are a significant part of the teams DPS in fights. You scale incredibly well with items, to the point where you are encouraged to buy only one defensive item.
Item variety is complicated by Bloodthirster being the only generically relevant defense item that your class can use early to mid game. Last whisper is required, as your role requires you to deal damage to their WHOLE team, and you don't have true damage(unless you're vayne or Corki). Infinity Edge also feels required, as a large amount of your damage comes from critical hits, and it's a unique source of a damage multiplier. Aside from a few triforce, blade of the ruined king, or Bloodthirster Kalista(which I think was patched out by Riot) builds, you build damage.
Aside from being expected to consistently maneuver to deal damage and survive for as long as teamfights persist, you also heavily rely on your teammates for everything. Your support peels for you. Your AP carry takes out threats to you. You probably have a fighter pulling threat from you by being an immediate threat for their team to deal with. You might even have another tank peeling for you with your support. Someone else on your team(with few exceptions, Ashe comes to mind some of the time) will be initiating. Even if you CAN initiate, you rely on teammates to follow up so you don't die to a sneeze.
Anyone on your team makes a mistake, and you could just die immediately from it. Rengar just distills the frustration of what it's like to be an ADC into a single kit. Everyone has to protect you, and because of that, someone making a mistake means you just die. Sometimes someone DOESN'T make a mistake and you die. Because the ADC is 'important' like that.
I really hope that Riot marksman itemization changes can help with that, like the juggernaut changes did. Looking forward to them coming out very soon. I'd be happy even if damage is nerfed(part of the problem is ADC vs ADC feels pretty random as well).
"Eternal life, endless torture"
Pretty much the only ADC I know of that can get away with building tanky. You're not a real tank by any means, but you can use your ult, swap into the middle of the enemy team, and not die immediately afterwards.
or a
jumps at you and you don't get peel.
and adcs would have a better chance at living