My father was an AF pilot for 20 years. I've never known a more conscientious and careful man.
One day he was going through the landing checklist, and was interrupted by a radio call. He resumed the checklist, then was told by the tower that he was attempting to land with the gear up. The interruption had caused him to skip that step on the checklist.
After that, whenever he was interrupted in a checklist, he started it over again.
I've been flying a somewhat large UAV lately, and inspired by the "real" aviators and The Checklist Manifesto, I put together a series of checklists. One for packing, one for pre-flight, and a mission-specific one for the day.
Early on I was pretty lax about following them, and inevitably something bad would happen. I'd forget to pack something and not realize it until I had driven an hour. I'd forget to check for loose bolts and lose one. Or I'd completely forget one of the objectives for the day and have to go back out.
I've tightened up my process quite a bit, and do exactly what your father does: if I get interrupted, I start over. It's mentally hard to do when I'm already feeling late, but I've come to the conclusion that that's exactly when I need to be more disciplined about it; that's when you forget things!
A little anecdote about the careful part. He flew ground attack missions in the Korean War. He didn't win any popularity contests on the ground. The leader for his squadron was one of the popular pilots. But when they were out of sight of the airfield, the squadron leader would radio my dad to assume the lead. He'd lead the squadron in and out, and when they got back near the base, he'd swap positions back with the actual squadron leader.
The reason was pretty simple. He'd take the time to pour over the maps and intelligence to find the safest route in and out, and they'd get back with the fewest holes in the airplanes.
I.e. when it counted, the squadron would entrust him with their lives.
I don't think it's possible to have a greater honor.
I've seen the same principle at work in a pretty different activity: rock climbing.
There's a well known story of one of the best climbers in the world getting approached by someone while she was tying the rope to her harness right before a climb. After a brief chat she proceeded to climb the route, lean back on the rope, and promptly plummet to the ground.
After being interrupted she had forgotten to finish tying a knot she had done thousands of times before. It's a good reminder to avoid letting yourself get interrupted in the middle of simple but extremely critical tasks, it's just so easy for the brain to skip over part of the process it knows well and consider it done.
Proper climbing procedure states that partners should check each other's harnesses and the rope to make sure they're connected to the same rope, the knots tied properly, buckles are double-backed, etc.
I had a similar incident many years ago where my partner only tied into one harness loop. Luckily it was in the gym and she wasn't on lead, but after that, I always make it a point to thoroughly check my partner's equipment.
One day he was going through the landing checklist, and was interrupted by a radio call. He resumed the checklist, then was told by the tower that he was attempting to land with the gear up. The interruption had caused him to skip that step on the checklist.
After that, whenever he was interrupted in a checklist, he started it over again.