Risk
Risk, its assessment and mitigation is a science all of its own. Let you give me an example from my company, a major international carrier.
- A request is received from a major airport for a display from one of our aircraft. After careful assessment, 2 ex-military display pilots are tasked with planning and flying the display. It is practiced in the simulator and air and supervised throughout by management. The display goes off flawlessly. Result - 2 pilots satisfied with a job well done, kudos for the company and 10,000 happy spectators
- On a delivery flight, a management pilot, with no display experience, decides to do a flypast on departure. He beats up the airfield at 75' and max speed with 30 company personnel down the back. Result - one pilot fired, one disciplined, a FAA investigation and embarassing video on YouTube
In both cases, the risk was the same - a display in a large twin-jet. But it was managed in totally diffferent ways with totally different results and totally different levels of danger. That illustrates the difference between the two - danger results from unmanaged risk.
To manage a risk, you have to recognize it. In the second case, the pilot didn't have the background to recognize how risky his manoeuvre was. I have lots of military and large civil experience but little GA time. I was talking to a GA pilot who was telling me how careful he was and then proceeded to relate tales of things he routinely did which made my hair curl!
Few accidents are the result of one thing. At any stage, the chain can be broken. In the experimental world, there is less chance to break that chain because the builder, maintainer and pilot are generally the same person. So if he lacks the experience or correct attitude, then any error is much more likely to get through.
As to the original question - "When do you walk away?". I believe that, statistically, you can go your whole flying career without an accident. So if you have one, you can maybe count yourself unlucky. If you have had two or more, I'd say that aviation probably isn't for you.......