Java's eccentric uncle Objective-C called this method "description" instead of "toString". That was a better name IMO because it avoids the suggestion that it's some kind of canonical string representation.
The language documentation does make it clear what toString() is for. And it's convenient to be able to (for example) stick objects and strings together with the "+" operator and have conversions automatically happen.
But (understandably) not everyone reads the language documentation cover to cover before they start writing Java code, so you can't count on that making it obvious.
Cover to cover would mean understanding the memory model and maybe garbage collection. That's too far certainly but a few basics would do no harm. toString is surely one of them.
Most Java developers I know consider rolling your own multi-threading scheme about as wise as rolling your own cryptography, and just pretend notify/notifyAll/wait don't even exist.