Trading Kills With Someone is NOT a good thing.
Disclaimer: It is better than getting nothing but just read and hopefully you'll understand what i mean.
You know the drill, when your in lane and you fight your opponent or you get attacked by the enemy jungler when your alone(It's not important why right now.) you die, but you kill the enemy too! Your happy! "Atleast he didn't kill me and get away with it." but, there's only one issue. Does that champion that just killed you get more out of a kill than you do? Let me explain.
What do all of these champions have in common? Well, you might say their "Assassins" right, and your only half right, two them can be Fighter's as well (Kayn and Riven.) but what they do all have in common is simple. The ability to get fed from just a few early kills and steamroll the game out of control, i main 1 of these champions, evelynn. It's really easy to get 3 kills with Evelynn, if you get them early enough your basically a one shot stop in every lane.
Kayn has a harder time doing this in some cases because he might not get his transformation even with a couple kills, it takes time, but if you get it early let's say at 8-10 minutes(Normal is about 12 i bet.) at this point in the game your unstoppable, but wait! Didn't i kill him back? How come he's so strong when he's 3/3/0? It's because he scales differently, if your say a Lucian, or a Caitlynn infact most ADC don't scale very well until later in the game and just having 3 kills won't be enough to give you the gold you need to stop an Assassin or Fighter that has the same ammount, they need less gold to one shot you, than you need to stop them from doing it.
TLDR: It's best NOT to try and go even whenever necessary, if you decide that "Going Even" in kills with someone is enough, then against a lot of champs out there, you'll eventually lose. Always strive to be better than your opponent, don't let them get anything out of you, that's how you wind and that's how you climb.
Prime Example: https://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2687288463/231258967?tab=overview
In this game i was Evelynn, now you may say that "Wait your 13/10/5 aren't you feeding?" well, yes and no. If we look at the graph we can see that until 15 minutes into the game i was actually not feeding and my score was actually 6/2/? this where things got hard for me and the rest of my team. We kept going even with kayn, he'd get a kill but then we would to, i did my best to prevent it but more often than not he always got atleast one of us before he died. So his score before 15 minutes was 9/4/? so he had 3 more kills than me, many more than most of my teamates and in addition stopped dying for them once he reached about 6 kills. This means he's fed as fuck boy, and despite the fact that he was initially 4/4 he hit his spike and we can't touch him anymore, his ending score over a 30 minute game in which he dominated was 20/6/6, all because we decided that going even early is fine.
