Only taking about champion and legend, where going down once puts you on deaths door, going down again during that state without you healing yourself kills you immediately. Commonly referred to as “grey”.
I have seen alot of people using healing supplies on legend when they were not grey, simply on low life. No horde was near, they were in no danger of dying anytime soon. This waste of healing is what gets people killed, and should be explained in abundance somewhere before even unlocking champion, because it becomes very relevant there. Recruit and veteran teach you very bad habits with the overflow of healing and being allowed to go down more than once before dying.
The character voice lines also dont help at all, telling players on low life to heal themselves.
Another thing that should be taught is that bandages are more important to carry than healing draught, especially if the other three players are carrying tomes.