Buddy checks and self reliance are not mutually exclusive..
I'm going to tell you guys a true story. The names have been changed because these guys still dive. I heard this story from the horses mouth and even though us New Englander's love to enhance our stories, this is pretty much how it went down.
Bill has lots of experience shore diving in the North East of the US. He has over 100 logged dives, done the rescue and advanced courses with his best friend Teddy. The two of them were inseparable, both in their 50's and became friends through their open water course not very long ago. Bill was an avid photographer and one day his wife bought him an underwater still camera. Bill couldn't wait to try it, but his buddy Teddy was ill that weekend. He called the local dive shop and hooked up with a group going to a site Bill knew very well. He rented tanks because Teddy was his tank supplier. At the dive site, Bill was very excited and was playing with his new camera constantly. He was buddied up with someone his own age, but Bill was so busy playing with the camera, he didn't have much time to talk before entering the water.
The group swam out about 100 yards from the shore before descending in a group. Bill was the last one down and once the group leader saw everyone was down, he turned around and started swimming. Bill of course was the last one in the group and the moment he saw something cool, he slowed down and took a picture. It didn't take more then a few minutes for Bill to realize something was wrong. The hose on his 2nd stage was getting shorter and shorter, eventually popping the regulator right out of his mouth. Luckily Bill didn't freak out, he stayed calm, reached around to find there was no tank behind him! He grabbed his air 2 octo and was able to breath off it, but he started to panic. He looked up towards the surface and started swimming. On the surface, he was frantic because the tank was putting so much force on the inflator hose, it was hard for him to hold onto it. In a last ditch effort, he held onto the inflator button and finally calmed down. His heart was racing, but he controlled it quickly and started swimming towards shore. In the calm shallows, he pulled the BC off, pushed the tank right back up into the bands and tightened it back down. He was more frustrated then anything else.
He turned around and headed back towards the group, which was marked by a dive flag. He descended and got right back into line with everyone else. Nobody had bothered to turn around and look for him, they didn't even know he was missing. Within the next few minutes, he found a skate going along the sandy ocean floor at a good rate of speed. He chased after it, unknowingly headed away from the group. He snapped his picture, looked around for the group, but it wasn't in sight. Since he was only 40 feet down, he decided to surface. He found the flag, made a compass reading and dove back down, using his compass to find them. As he swam however, he noticed it was getting harder to breath. He shrugged it off as perhaps being his heart rate being higher from all that swimming chasing the skate. However, he went to suck on his regulator and it was way worse. He looked down at his gauge, zero PSI. Bill immediately shot towards the surface, swimming as hard/fast as he could. With a huge gasp of air, he erupted with a splash, panting from being scared and working his body so hard. He floundered around, trying to orally inflate his BC, which he managed to do. He just lay there on his back, trying to calm himself down. Being an analytical guy, he went through everything that happened in his head, but couldn't make sense of what happened. He made it to shore, put his tank down and turned the tank off. He noticed it the knob only turned a tiny bit. Bill couldn't believe what he felt, this whole time, he was diving with a tank where the valve wasn't fully open. When the tank ran low on pressure, there wasn't enough pressure to push open the 1st stage position.
Moral of the TRUE story?
Bill was an excellent diver but because he was reliant on other people, he never fully understood a few basic points.
Bill's friend always supplied the tanks. Bill never bothered checking the tanks because his buddy took care of them. What Bill didn't realize is that he was diving with HP steel 100's in the past and the rental tank was a LP 80. Even though the tank was physically the same size to Bill, the manufacturers were different and the diameter was slightly different as well. He didn't even think twice because he simply had no experience diving with any other gear because everything was taken care of him by his buddy. Also, because his buddy always checked his gauges, Bill used that as a reminder to check his own. Without his buddy around, he simply assumed the tank's he rented would last him the same time as the tank's he was use to diving. Bill's tank valve catastrophe was simply bad luck, a combination of the valve closing as it went through the straps and when he grabbed it to pull it back up again. He should have exited the water, gone onto shore, checked over his gear and waited for dive two.
These are the kind of things you learn when you're self reliant. You focus on gear much harder because you're use to dealing with it, instead of it being supplied to you. In solo diving, you bail out of a dive if there is any technical issue, return to home base and go over what happened. With buddy diving, you're so use to someone else being at your side, you become over-confident. That excess confidence can lead to issues, like the one's Bill had on this day.
Bill continues to dive and I ran into him last summer in New England. He's 62 years of age and finally own's his own tanks.