Just read a bit of Neil Williams' book, and I noted the following point that would emphasise the nature of stress and microfails etc.
The Zlin aerobatic aircraft had an airframe life of 2200hrs when subjected to +6 and -3G aerobatics.
The same aircraft, when flown to higher unlimited aerobatic standards of +8 and -6G, was reduced to an airframe life of only 100 hrs.
Added for your interest.