I've done it.. yep... even on purpose some times. Hold the door open so I can fit my ego in... okay
Nearly all (probably all) instructors have dived "solo in a crowd". Every time I take group of new students out on an ocean dive, I'm worse than solo, I have multiple new divers dependent on me who generally would be able to do nothing for me if I got in trouble. Well, you might say, you have a DM there, they could help you. I say... NO! I want my DM, or if I'm lucky, co-instructor to take over command of the class and I will resolve my problem myself.... sounds like ONE def'n of solo diving to me, but I suppose that's a situation that is not true of the majority of solo divers.
It's my belief that all tech dives should be planned as if it they were solo dives, with a backup brain (buddy) along for appropriate safety/fun/comraderie. But if something happens to your buddy, God forbid, you may likely end up finishing your dive (deco more likely since you should abort the dive) as a solo.
Not surprisingly soloists also stretch other rules such as streching gas supplies thin, diving to deep for the mix, cutting deco short.
I do take exception to Tick lumping solo diving in with some obvious examples of poor planning/training/death wishes. Show me the statistics that prove that well trained solo divers with their heads screwed on right (yes there are some!) routinely violate such basic safety rules. Dive too deep for your mix, and as someone put it, your buddy has now taken on the task of body/gear recovery.
The person who stretches those kinda rules will likely be just as dead even in a crowd. Matter of fact, I would bet that any diver with a reputation for that kind of dive mentality might not EVER find a buddy willing to dive with them twice, so they either have to get smart or get some training, barring that, they will probably dive solo until fate/karma/Darwin catches up with him/her.
Of the five major contributory factors that kill tech divers solo diving is right up there.
Sorry, solo diving doesn't kill divers: poor planning, diving beyond your training, inadequate/improper gear, insufficient gas, insufficient/no reserve gas... those things kill divers.
You should be diving with less experienced divers to share your knowledge and skill.
How would the local Golf pro feel if you asked to tag along for 18 holes for free, asking alot of questions, wanting advice on every shot, wanting to know what clubs to buy, what grip to use.. yadda yadda yadda Or how about the local ski instructor, private pilot instructor... you pick one....
I'm sorry Tick, but I don't pay oodles of $$$ for a nice tropical dive vacation to spend time teaching you, or anyone else the finer points of diving. I'm lucky (blessed really) to have a wife who is also a very experienced diver and instructor whom I love to dive with. If all buddy diving was like diving with her, I'd never have a reason to dive alone. Sometimes however, say on a week long liveaboard, if she wants to sit out a dive and tan, I have no problem going solo, but that's my choice and it's not for everyone.
As Tick implies, we can all learn something new on every dive. I agree wholeheartedly. I would say that I learn new things even diving solo, but I also seek out divers more experienced than me. The difference for me is that I will willingly pay for their time in the form of continuing education and advanced training rather than glomming on to them as a less qualified buddy on a dive hoping he/she will teach me something for free. That's not to say that an instructor or highly experienced non-instructor might not mentor someone out of the goodness of their heart, but sheesh people, have some respect for the time, $$$, and effort that an advanced diver (especially an instructor) has put into their education. "You get what you pay for" applies equally well in the world of scuba diving.