99% of the time, people think that the expectation is obvious, that it was already discussed, while in reality it's probably not true. Deliberately setting expectations of what you expect from people, and what they expect from you is important for a successful outcome.
A good expectation is the one that matters.
For example, if you are a marketer, the expectation is that you should be able to measure your work. If you can't quantify your work, you won't be a good marketer. At the same time, a good marketer should not be expected to be good at shooting great videos.
The best expectations are set based on the role for which they are set, and they are very detailed in such a way that cannot be misunderstood.