It's quite possible for more than 50% of people to be above average drivers. If there are 100 people, and 80 of them cause no accidents, and the other 20 cause 10 accidents each, then there are 2 accidents per driver. 80% have less than average accident rate. By the same logic it's possible for most people to have a below average salary. Once extremes are possible, then averages start being less applicable.

However for things that have no extrmeme (e.g. height, IQs), the above average and below average rates are similar.,