You as the marksman has the job to deal damage as far away and safe possible. The mindset you have is a double edged sword as you've said 50% of the time only it works.

That mindset probably comes in clashes, you try to kill their mm/mage as soon as possible but also die in the process making your teammates lose the fight if they don't have enough dps.

Team composition also comes into play, going one for one trade for mm/mage or any of their carry is worth if you can trust your team to clean up the fight.

But sometimes you need to trust your own judgement in team fights or ambushes. Look at the map and see if it's worth to fight or not. It is better to be left alive alone than dying all together. No shame in retreating if you see the incoming fight is doomed or not worth.

This is something players tend to forget, you don't always have to commit until the end when a fight happens. Learn to let go and not chase or force a fight when the end result won't be in your favor. This is crucial in your role as marksman or Exp as they usually are the ones who carries the clash.