I've only got about 35 dives under my belt. On my first real dive trip I decided after several dives it was best to setup my gear and not just double check it after the DM's set it up. The first issue I ran into was when DM jammed my new wing between the tightly racked tanks of mine and my buddy's tanks. On another dive I shutoff my air 'cause of a bad o-ring and I and no one else had a spare (another lesson learned). When the DM was helping me kit up they stated air was on, but clearly my pressure guage said it wasn't. DM assumed as they usually setup all gear my air was on. I make a habit of double and triple checking before I jump in but those couple of incidents showed me early on how one can become complacent by having someone else setup your gear.