For our economy and society (and health service) to keep rolling along as close to normal as possible, we must have very low levels of virus circulating. This means everyone trying very hard to avoid spreading or catching the virus, regardless of whether they themselves are more at risk.
It needn't mean extreme social distancing, so long as we only relax restrictions gradually, once we're sure local rates are low, and don't get ahead of ourselves and all stop trying before local rates are low and testing is working. Lockdown is temporary, but if, say, all the people under 50 stop bothering with any precautions other than washing their hands, then it might have to come back.
It can't just be about individuals assessing their own risk. Look at all the cancer consultants who are aged over 50 - they can't suddenly stay at home, if you want people to carry on getting cancer treatments. Look at all the grandparents who provide childcare so people can work - they can't do that if there's lots of virus circulating. We need a collective effort to avoid catching and spreading the virus, regardless of what our own individual risks might be. That's how we'll keep rates low, and when testing and tracking kicks in, we'll be able to squash local outbreaks fast, and keep them low.