Assumption, the mother of many disasters. The word has been used a lot in this thread
When I was in flight training (dual), quiet regional airport, no overlapping chatter from other CTAF's, gave a call" VH-xxx, C172, entering downwind, runway 21, full stop". Gave a further call turning base, all very correct. Then had a reply from a C402 downwind same runway. I was focused on the approach, instructor advised me to proceed, , while looking out for the other aircraft. I had aimed for a touchdown on the first jet marker, which I duly made, only to have said 402 nearly give me a haircut
as he went around over me.
He came into the flight school later, with his explanation being he had "assumed" I would land long and vacate the runway promptly for him to land. Given our relative speed differences, this was most unlikely to happen even if I had landed long, as he has "assumed" I would.
Some assumptions are safer to draw than others.