I always thought that was a bit of a dodgy concept ... For example - if you slipped off a railway platform and were hit by a train which lopped off your legs, and then the ambulance taking you to hospital crashed causing you a serious brain injury, and then in hospital they gave you a transfusion of the wrong type of blood which damaged your kidneys, but the doctors somehow stopped you dying ... how strong do you think you'd feel then!
(I do agree that overcoming adversity can increase one's mental fortitude. I've had a difficult time over the years but still manage to get on with most of the challenges that I set myself.)