This is true but it's just not realistic. There are situations in life where expectations are totally appropriate. I'd even argue that expectations drive us forward. And if you have no expectation of an outcome, how can you be happy or sad at all at the end? Or how can you tell there has even been an outcome? If I have to drive somewhere and have no expectation of arrival time then I'll neither be happy nor sad when…
"[...] plow through and find some happiness or a silver lining"
What you're suggesting here is that happiness has to come in bursts (for lack of a better word). While I think that can be true, I believe the kind of happiness the OP is referring to is more deep-seated. By no means does it exclude other emotional states, but it reduces anger to a minimum. Although "Disappointment, heartache, sadness, and gloom" may be constructive, I honestly don't think anger is.