Some of the causes I can think of are inexperience (although I could never accuse Mary of that), not trusting your own abilities, not trusting other boats to keep a lookout, not trusting the other boats know when to keep clear, not trusting the other boats will try to keep clear, not trusting the other boats are capable of keeping clear (you know, the magnetic attraction of fiberglass).
Is it simply a matter of relative boat speed, size, and testosterone level, or is there more to it? What can we do to not frighten people off the racecourse?
This is getting confusing because posts are crossing. However, it definitely is an issue of boats of greatly disparate speeds. And it is also an issue of not trusting the faster boats, especially those with spinnakers, to watch out for, and try to avoid the slower boats that are going in a different direction and do not have the speed and agility to take evasive action, whether they have right-of-way or not.
