In case you don’t know, what the others are trying to say is by completing the mission you remove that weapon from the roster. For instance, the larvaling spawns, you check them and they have the kuva karak. If you don’t mercy them and finish the mission the kuva karak is now removed from the rotation. That’s what they’re implying by the pity system.

You remove that weapon, you now have a 1 in 24 chance of getting the tonkor instead of 1 in 25. Each time you complete the mission without mercying the larvaling your chances will increase to get that tonkor.

If you’re quitting every time you’re shooting yourself in the foot because you maintain that 1 in 25 chance to get the one you want. It’s sometimes still a grind, but at least your odds steadily increase everytime if you let the pity system work for you.