Another factor is that each individual may have particular strengths; one may run very fast on a track, but slow down dramatically in the forest; another may have no great turn of speed, but chug away steadily uphill; still another may have no confidence in her ability to follow a compass bearing, but may be able to read contours very well. Hence the choice of a route on a given leg between controls may have many possible "best" solutions. This also means that the best route for a beginner may not be the best route for an advanced orienteer. As an example, the map shown here gives the route choices and variations taken by the top orienteers at the Swedish National Championships some years ago (recall that there are about as many Swedish orienteers as all other countries combined!). Each orienteer's route is shown as a single red line and, at places where several individuals went the same way, red numbers show how many orienteers followed that portion of the route. Some fields (yellow) were out of bounds because crops were growing and are marked with red cross-hatching. Although this is perhaps an extreme example, it does show the variety of routes (and combinations of subsets of routes) that may be possible on a single leg!
Navigation in orienteering can be reduced to two factors: Choosing one of the many possible routes to the control
Finding your way along that route
Once you have learned some basic techniques and rules of navigation, it should always be possible to find the control - given that the map is accurate. Therefore, much of the variation among individuals' times may come from their choice of routes. This is particularly true when speed through the terrain varies dramatically in different places, which can occur for any number of reasons: A path is faster than the woods
Vegetation mapped as green may be very slow-going
Going uphill and then down may be slower than going the long way around
A potentially faster route may offer no navigational aids, while a longer/slower route may provide a navigationally easier approach to the control site