Low expectations are often a self-fulfilling prophecy. We insulate ourselves from failure, don't try as hard, brace for the worst and often get it.
High expectations, on the other hand, will inevitably lead to disappointment. Keep raising what you expect and sooner or later (probably sooner) it's not going to happen. And we know that a good outcome that's less than the great one we hoped for actually feels like failure.
Perhaps it's worth considering no expectations. Intense effort followed by an acceptance of what you get in return. It doesn't make good TV, but it's a discipline that can turn you into a professional.