I've been a ham for 53 years now, probably observed my first frequency first in year one or two when I tried to transmit on a frequency the SSTVers used and when two nets on 40 SSB disagreed who was too close to whom.
In contesting, calling CQ is the fastest way to score points, but is only room for a certain number of stations to be calling CQ on any given band while not interfering with each other. If 40 CW is 100 Khz wide, and everyone stayed 500 hz apart, 200 stations can be calling CQ. When the 201st station tries to wedge his way in, frequency fights often occur.
I had a back stage tour of the indoor rain forest exhibit at the Baltimore MD aquarium. To assure that some birds are in the air at all times (to please visitors) they have enough trees/branches such that only 90% of the birds can fit to roost at any given time. When one of the 10% up the air wants to rest, he has to wedge his way in and the avian equivalent of a frequency fight occurs!