Exhaustion is a potential weakness and danger to witches and warlocks while performing magic. In order to perform magic, witches need to channel magical energy from themselves and possibly their surroundings if their own power is not enough. When witches or warlocks perform very powerful magic and are pushed beyond their limits, they risk exhausting themselves.
Performing magic puts strain on witches to the point where channeling too much can weaken or hurt them physically. Channeling too much magic may lead to bleeding, loss of consciousness and even death if pushed too far.