Human body is antifragile. After experiencing a reasonable amount of stress, and fully recover from it, we become stronger than before the stress.
Normal functioning - to experience short-term stress (physical, cognitive), then allow your body to rest.
The most important - to keep the balance.
If we never stress - we start degradation:
If we always at stress without recover, we start to burnout:
And if we balance, push a bit out of comfort zone, recover, then push again, we improve: