Good point Magnus. I biked to work for many years, for several crossing right through central London in the rush hour. I know about defensive riding, and assuming the other guy is a homicidal maniac. But I also used to fly light aircraft out of and around a US Airforce base, and I know the issues facing pilots of light aircraft when mixing it up with fast jets. But nonetheless, once you're recognised what factors you're faced with you have to modify your behaviour to try to deal with them. I was involved in one "air miss" when but for my extreme avoiding action I would have hit a passenger jet descending over central London, but I was in radar-controlled airspace and they (ATC) screwed up (I wonder how often that happens?).
Rather off the point of this thread. But it illustrates that when operating dangerous machinery (a plane, a car, a boat) you MUST be aware of how other people might behave with respect to your machine and what their capabilities are, and similarly when operating near significant machinery you must be aware of what issues the operator of that machinery is having to deal with. You MUST recognise that a driver/pilot/boat captain may well have blind spots and ensure you don't put yourself in those blind spots. And that a boat (say) needs time and distance to take avoiding action, and that time doesn't start until the captain has seen and comprehended the obstacle (which may be you).