As a recreational diver, I have often been paired with strangers. During one dive, a buddy got into a foot first ascent and did nothing about it; he didn’t even seem aware that he was in trouble. Although I had much less dive experience than him, I had to grab him, flip him over, and help him get rid of the excess air. During the post-dive discussion, it was evident he had no idea that there had been an issue underwater. This told me that he hadn’t received proper training on the safe use of a drysuit.
I occasionally work as a diving guide in cold water and have found that some clients do not keep track of their air. Despite my pre-dive reminder to do frequent air checks and to surface with no less than 500 PSI, one client accidentally let his air pressure drop to 400 PSI. He only discovered this because I was performing a group air check. While diving in the tropics, I have found that some divemasters do not perform air checks with their clients; they just expect each client to ascend once they run low on air. That particular diver could have easily run out of air if someone else hadn’t been checking his air for him.
It is ultimately your life at risk if something goes awry. If you are in the mental state that you may need to act as a rescuer at any moment, you will quickly realize how important it is that you are in a safe situation yourself in order to be capable of assisting your buddy. Whether your buddy is a dive professional or straight out of their open water class, long time diving partner or stranger, it is vitally important to take responsibility for your own safety.