League of Legends (LoL) Question: Safety over aggression?

If you're InSecing the enemy ADC into your team, then dying in exchange for that is definitely for the greater good. Of course, generally a tankier build is built on Lee so he can survive going in.

Know when you can and can't go in. There's a word for Lee Sins that follow up every Sonic Wave, Lee Syndrome. Don't suffer from that. Know good and bad engages. It's a matter of experience, knowing your own limits and the enemy's limits. The games with less deaths is probably against an enemy who isn't so single-target damage focused, and can't immediately kill you. Hence, the experience is needed to judge the situation.

Personally, my general rule is simply just try to die as little as possible. If you reduce your deaths, then you will get better results. It's common sense, really. Late game, your life isn't worth it if you can't exchange it for a higher priority target on the enemy team. If you can get an inhib tower just before you die, good for you. Now your team is down one person to defend. It really isn't sacrificing yourself for things such as that.

So to summarise, just know what you and the enemy is capable of doing. Assess the situation before you follow up that Q, and don't play impulsive. If you know the situation you will be placed in, you can judge whether the outcome will be worth it for you.

You want to see if you have an opportunity, for example is somebody out of position? Are they peeled? did somebody overextend? if any of those is true then you want to try and slow them or kick them if you need to. Of course there are instances where you have to play very aggressive if you have the oppurtunity to say kick the enemy ADC into your team late game but you wont always want to just blindly dash into the other team. Theirs a balance between safety and aggression that you should be able to find at some point. Once you get to that you should be pretty pleased with yourself, usually it results in substantial amounts of LP.

Sorry if this was a bit cryptic but the idea of safety vs aggresion is a difficult thing to describe.

You need to be able to identify the proper situation in which kicking an enemy AD back into your team is proper. What you face is a common problem for up and coming lee sin players. Not every open opportunity to kick the enemy carries is proper, especially if you're behind.

Some good markers to keep note of are: enemy CC that can stop you, summoners on the enemy carries, dashes / blinks on the enemy carries, and cooldowns of other enemies that can potentially save the kicked carry.

It just takes practice after that. With experience you'll start to understand when you can and when you can't kick.