I am not entirely sure that this is the right thread to be posting this but since others are talking about incidents and experience I thought it would be worth sharing.
A wise person in gliding once described to me the dangerous times in a pilots career as 80 hours, 800 hours and 8000 hours.
80 Hours In gliding by the time you get to 80 hours you are probably early cross country with several hundred successful flights. A poor decision will put you in a situation that will test your skill to get your self out of. It may be misjudging the wind sheer on final and you land short or miss handling a cable break. The key factors here is that a poor decision leads to a situation where there is insufficient skill to rectify the situation.
800 hours By this stage you have quiet a few years of flying behind you. You are trying to fly further and faster and are perhaps competing in a few competitions. The reasonably high level of skill you have leads to complacency and higher levels of risk taking. This is reinforced by previous success, you were able to thermal away from 300 feet to go on to complete a 750km triangle. On day you get caught out, you fly too close to rapidly developing could and end up engulfed, you get low on a cross country flight and fail to pick a good outlanding spot in time. Complacency and Risk taking have lead to dangerous situations.
8000 hours By this stage you have been flying for 45 years. You learnt to fly at 20 and have been gliding ever since. Now approaching 70 things are beginning to slow down in flying and in life. You don't see situations developing as quickly as you used to. Your reaction times are slowing and you cant think about many things at once. An aircraft landing ahead of you and still being on the runway distracts you and you get slow turning base and spin in. It can be tough to give up what you love but flying beyond when you are safe is unsafe.
Now the risks are slightly different between RAAus and Gliding but I suspect that many of the factors above apply to flying ultralights too.