From what I've read (including on this site) ascending riders should give way to those coming down a trail/track. This seems counter-intuitive to me though, when one considers difficult climbs.

Here, the ascending rider is doing all the work, having to work at keeping a smooth rhythm, trying to stay on a decent line, dealing with loose stuff that can throw the bike, ...

The kind of climbing one finds on the Oaks, for example; steep, loose and bumpy. Where, if you stop for any reason, it's difficult to get going again.