I agree with the statement that "You don't know what you don't know". That is the risk, however its like exploring, one step at a time and you feel your way, yes it has risk but its calculated risk rather than rushing in head first all the way. Yes you can get caught out, and yes you could die.
My experience was to go to Truk lagoon with little knowledge of the diving other than its a great place to dive and heaps of wrecks. I was expecting all this information from the tour leader in a meeting which did not happen before we started our three month holiday. It was only just before I left for Guam that the tour leader emailed me and asked if I was diving twins or singles? I advised I had no experience in twins so would have singles. I then emailed Truk direct and started finding out more about the diving conditions, depth etc. I then sought detail about depths and conditions.
On getting there I discussed with the dive master there and we decided on 15 litre singles and a 6 litre sling tank with 50% Nitrox slug at 5 m under the dive vessel. Most of the dives we to 45m or less however we were facing a couple of 55m dives. I discussed this with my wife and we decided to do the following;
Let the group dive to the depth and time they wished (to prevent us being an issue and spoiling their dive)
We would go down at our rate and to a depth we decide and would stop our dive at our time rather than to feel we had to stay with a group.
Ensure we would not breach 55m
Ensure we would watch our air and abort at anytime we felt things were not right, no repercussions.
We would dive the plan and follow our deco plan and add some as a safety margin, and would also use the 50% nitrox for 3 min after finishing our (extended) deco
We did the dive and several other dives always following a dive plan and enjoyed the experience immensely. Funnily enough we always came back with more air that the guys diving twins. I might add that 90% of the group had no training in deco, advanced nitrox and little if any in twin tanks. This I think reflects on the tour leader. Some people only had about 25 dives up. I had knowledge of MOD, narcosis and air calculations, SAC rate etc so felt reasonably comfortable and did realise there is some risk involved. We have also done many dives to 40m.
As an example in using ones head and diving to ones ability, on the first dive for us, we dived a wreck but they had organised 2 groups to penetrate. One in one side of the hull and another in the other side. Meet somewhere in the middle and pass by (fraught with danger I think). Anyway we were the last to enter and the other group had already come nearly all the way through. It was a great muddle up as we met (as to be expected) and we found ourselves not able to see our group when passed the other group. We could have continued and guessed our way through and hoped to see a light but that was just stupid, so we turned around and came back out with the other group and went up and over to meet our group on the other side. Now that planning was just plain stupid. A diver with little experience may have tried to continue and would most probably got lost. It was experience and using a safe diving approach that stopped us from continuing. A lesser diver "doesn't know what they don't know, often until it is too late.
On my return home I recognised we took some risk and thus needed further training to reduce the risks of deep diving so completed Adv Nitrox, Decompression theory and doing extended range & Trimix. In looking back on our experience we had covered most of the requirements for deep diving, but perhaps needed more redundancy and larger sling tank or twins and sling.
So I guess in summary I would say;
I do recognise without good training we really "dont know what we dont know" and that's a very real risk.
Whilst that may not prevent us from pushing boundaries, read up and do it slowly if you cant get the training, DONT RUSH AHEAD AND BE A STATISTIC. Become knowledgeable as much as possible, don't be lazy and not make an effort.
Understand the risks and their impact on you and your buddy, don't just ignore them or "Murphy" will get you.
There is a point where experimental becomes stupidity, recognise it and don't go there.
There is no underwater police so you know you can do anything, also recognise there is no underwater emergency 000, so you are on your own