There are a lot of people out there who have given up on using a traditional bicycle. There are many reasons for this, but the most common involves an injury sustained by falling.
If you are especially unlucky this can happen even if you are wearing a helmet. But this doesn't have to be a bad thing!
Upright exercise bikes can be an excellent substitute for cycling-related activities, because a good one can give you just as much of a workout. Moreover, they are much safer than a bike.