Becoming the second victim

[D_B]

...
Heading stuff off before it gets to be an emergency is good part of the training you get in a Rescue Class , but sometimes that is not possible ... you react when you decide to help, and tailor the help you can give, to the situation as it unfolds .. like trying to reach someone going down or up, and calling it quits after ascertaining that the risk has just become too great

If your buddy is already bolting for the surface or sinking off into the blue, you already missed the signs that he was having problems.

you are correct , and I would severely inspect the situation afterwards to see what I did not notice or dismissed
But .. in the part you quoted I was talking generally .. sometimes you don't/didn't ever get the chance to head anything off before hand, and your forced into dealing with it as it unfolds