When I first started dating my husband, he told me that he prefers to keep his expectations low in order to avoid disappointment later. Naturally, I applied his words to myself--like any self-centered young adult--and was rather offended by the implication that he was having low expectations of me. I've since come to understand the wisdom of his philosophy, although I still make efforts sometimes to help him feel greater feelings of anticipation about an upcoming event (e.g., vacation, family outing, reception for work, etc.) than he would on his own.
His "low expectations" are usually very realistic expectations based on his experience and knowledge. He still hopes for the best, but he doesn't have a mental picture of everything turning up roses all the time...and that's a good thing, for although I'm a good wife, I'm not a "10" in the figure category (thank you, four pregnancies and sedentary work), and I spent much of the past summer in a semi-invalid state complaining about nausea. Yet, he still loves me and thinks I'm great. I consider myself very blessed that my husband doesn't have expectations of me being a superwoman, for I could not measure up.
I used to think one of the things my parents did "right" was have "high" expectations for us academically. I've since come to realize that what I thought were high expectations then were actually very realistic expectations given the academic abilities of my parents (father is now a PhD/MD, mother is a PhD/JD) and the early education they gave us (they ran a private school based on traditional academics when I was in pre-school). When it came to genetics and environment, they bestowed a good hand on me, and they were just expecting me to play it properly.
Now my job is to learn all I can about the abilities and interests of the little ones I'm raising so that I can have appropriate expectations of them. Expectations that are too low are an insult and can lead to delays in their development; expectations that are too high set them up for failure and depression.