I've carried an M&P .40 cal every working day for the past 7 years. Before that, I shot single-action revolvers as well as other striker action SAPs. With the single-action, they were old-school, no transfer bar, so I never carried a round under the hammer.
With the M&P, I always carry, in a retention holster, in Condition 0. In the literally thousands of times I have drawn from the holster, I have never come close to pulling the trigger. Whether I'm drawing to unload, or drawing up on threat, my finger is nowhere near the trigger. It rest on the frame on the right side of the weapon, until I intend to shoot.
In my department, I'm aware of only two NDs in the past 7 years. Both where a person actually put his finger into a gap in the holster and pulled the trigger. Lesson, keep your fingers out of the holster, no matter how bored you are.
I don't consider myself to be an expert-level user. I receive bi-annual qualification training which consists mostly of clearance drills and hitting a very large target from close range. Every once in a while, the training will simulate firing from cover, firing in low-light (using tac light) or a hostage situation. I am a mediocre shot. Not a competition level shooter by any means.
I'm not sure why people insist that if a firearm is locked and cocked, it will fire without pulling the trigger. It cannot.