There are good arguments to support both sides.
On one hand perhaps you should lower your expectations because they’re too high. Examples of this could be expecting to earn £50,000 as a graduate with no experience or expecting a friend to reduce their rates even though you know the quality of their work will be more than worth it.
Then on the other hand, a reason not to lower your expectations is because you don’t want to get into the habit of settling. I think there’s a fine line between knowing what you want and expecting too much. Knowing what you want is great. Believing that it is possible to have more than you have right now even though it might take time is a pretty fantastic thing.
One of the most common reasons that people lower their expectations is because they allow the thoughts and opinions of others to convince them that what they want is unrealistic.
If that is the case, it might be worth being more selective about who you get advice from and who you choose to listen to.