Players making a single mistake that causes other mistakes in a snowball effect is the #1 cause of wipes. Followed in close second by simply not doing mechanics and only in a distant third, gear checks. Bad players usually consider the opposite, that gear checks are the #1 cause, but, you know, that’s why they’re bad.
The primary objective of practically any fight is avoiding chaos, and you do that by minimizing information overhead. Every time you introduce a new unexpected variable (change in CC needed, unexpected positioning change, emergency cooldown/consumable, sudden rotation change, etc.) you increase the risk of something getting out of control.