Until Damage gets nerfed down so teamfights last longer than 3 seconds, stop building on-hit...
Every time I see a Kennen, or a Kayle, or WW or someone that has natural on-hit damage, I always see someone grabbing Lethal Tempo and grabbing a Nashor's Tooth and maybe a Runaan's hurricane. I even see people using on-hit on characters like Ivern or Nunu. I've seen crazy folks go on-hit on Ekko of all things.
Seriously, stop being baited by that random youtube video titled "STOP PLAYING KENNEN WRONG! JUNGLE ON-HIT KENNEN IS UNBEATABLE" where someone goes 15/2 on Kennen with 
. If you saw it in a video, I am 100% certain that the player is Master or Challenger and they're playing with Iron players on a smurf account. Especially if the names of the players aren't visible.
On-hit builds are dead. They take too long to kill. It's why Machine Gun Lulu died. It's why on-hit Kennen died. Please do yourself and your team a favor and understand that if you're building on-hit, you're severely weakening your character.
....... Unless you're playing 
