Over-worked, under-staffed and under-qualified maintenance staff suggests under-paid maintenace staff. But none of that can in any way excuse not knowing how to, or worse forgetting to, fasten the cowls to the engine.
Excuse, No.
Reasons, Yes.
All of the criteria quoted above have been common factors in many accidents and incidents. That is why millions have been spent on Human Factors training and it is also part of the CAA Maint Licence syllabus.
Unfortunately, some employers choose to pay lip service to it.