Expectation is a strong belief that something will happen or be the case in the future. Setting proper and clear expectations gives clarity to both parties. You are not letting anyone down by properly setting expectations. This is just a simple understanding that you are on the same page.
Having a clear and properly set expectation is good. Giving others the context and intention so that it will be clearer and easier to follow. This is to help others understand the bigger picture. Having them understand the big picture makes them understand better and commit more.
Make your expectations clear to yourself first. It is difficult to build mutual clear expectations with others if you don’t know exactly what they are yourself. You have to determine also, where to have those expectations. Define the area of your expectation so it will become more clear.
Once you have set clear expectations, you have to meet and discuss. The other party also has expectations from you that you need to know as well. Meet halfway and arrive at a mutual understanding. In this way, you will not let anyone down because you have properly set expectations.