Mettle is a person's ability to cope and persevere.
Metal fatigue is when metal is stressed, cracks, and breaks-- sometimes with tragic consequences.
So when someone's mettle is exhausted, leading to personal breakdown, we can call it mettle fatigue.
The year of COVID-19 pandemic social distancing and isolation has led to near universal mettle fatigue.
Dealing with people's antisocial nearing results in mettle fatigue that might not even be comforted by the alcoholy trinity .