I had a signature that said I could fly a PA31 (after 1.5 hour training, with one engine failure at altitude) but wasn’t completely convinced.
So signed up to Vortex ICUS program to gain experience on a PA31 about 15 year ago.
Learned a lot - Chieftains, at night, IMC (down to minimas) full payload, minimum fuel….that sorts the men from the boys.
Went from someone who had a signature to fly PA31s to someone who could actually fly PA31s.
The lessons learned remain with me now.