Experienced divers also get complacent.
Only the other day, I was on the boat, with my wing on - leant out to wash my mask, overbalanced and went over the side. No reg in, no mask on and my fins on the boat. Not a huge drama apart from a bit of current meant someone held onto my rig whilst I put my fins on in the water listening to the (deserved) laughter on the boat.
Someone less confident might have been more flustered. However I should have, and do know better. Complacency!
Yes, I'm as guilty of that as anyone else, for getting a bit complacent and not doing things according to the rule book on occasion.
One advantage of doing a lot of my diving with a club, is that I spend a reasonable amount of time teaching, or diving with inexperienced divers. So I do try to be aware that my actions on occasion are copied by those with less knowledge.
The other issue I am very aware of, is that when you have very little knowledge the rules are very black and white. With knowledge, you start to understand the grey areas, or where the original 'rules' where to keep things simple.
As an example. If the rules say you can't dive deeper than 20m (66ft), then anyone can breath Nitrox 36. As a novice you are restricted to 20m, and can use Nitrox 36. but you have no knowledge of Oxygen Toxicity, and maximum PO2 etc. So 'if' you dive beyond your qualification i.e. to 30m+ (99ft) on Nitrox 36, then you risk Ox Tox' - a direct result of diving beyond the knowledge level you have.
On the amusing - but a demonstration of complacency.
A group of us (pretty experienced) where diving off a shuttle boat. A small boat shuttled us from the shore to a pontoon, where the larger shuttle boat was moored. On the second day, the smaller boat shuttle was a bit messed up. To avoid missing slack, we waded out to the pontoon, loaded the boat and went diving. After the morning dive, we waded back from the pontoon. Afternoon dive, we used the same technique to load the boat. On returning the shuttle boat was still missing.
A shorter member of our party slung his twinset on his back, stepped off the pontoon, and........... disappeared....eventually reappearing spluttering and yelling, his gas was turned off, no mask, no fins....down he went again.... up he popped, someone grabbed him and turned his gas on and inflated his jacket.
Whilst some think 1000 dives and an instructor qualification means you can walk on water -- he proved the opposite!
Once he was safe, he came in for a lot of stick for the rest of the season, and a few beer fines