6 Can all risks be avoided?

Our natural response to risk seems to be to avoid it at all costs. David explains why this may not always be the right thing to do.
[NOTE: We have recently discovered an audio problem on the first ten videos in this series, including this one, which causes the sound level to vary. We apologise for this problem and the video production team are trying to fix it. We hope it does not spoil your enjoyment of the video content.]