How do you keep your expectations low without just abandoning them completely?

I’ve seen posts here talking about how if you don’t expect much of anything you’ll never be disappointed. That makes sense and all, but doesn’t that also mean that you’ll never be able to hope for anything and always assume that the worst possibilities will always come true? There’s got to be some way to strike a balance…but what could it be, and how can I find it?

EDIT: I neglected to clarify that this means expectations of things other than oneself. Another person, a television show, a vacation, and so on. I will elaborate on my situation below.

A certain thing has met my expectations in many ways, and often surpassed them. Consequently, I raised my expectations to match the consistent results. Then in a certain situation where I had been given substantial evidence that those expectations would also be met, this thing failed to meet them in a manner I find inexplicable, especially because it was otherwise able to meet them in other respects.

The fact that it was a small thing that let me down thus only makes me more distressed instead of less, because I know for a fact that this thing could (and previously did) do better than it did. It’s as if I’m saying “well, I can’t trust my own experience and past evidence of this thing, I may as well stop trusting them to do anything but the bare minimum” despite knowing for a fact that they can indeed do more. My own effort, as far as I know, will have no effect- I have no direct contact with this particular thing and have no reason to believe that I can establish that contact.

And just abandoning expectations outright is not viable because it would require forgetting those past experiences completely. How is anyone supposed to do that?