...Or At Least In "Like"

Whenever I'm in a new relationship, I always assume that things are going to go well. Not like wanting to jump into marriage or anything, but just "rounding up": I assume we'll get along better and better (and feel closer and closer) as we get to know each other more. Of course it doesn't always work out that way - there's a million pitfalls that can derail the process. It's so disappointing when one of them happens (not to mention confusing when you don't even know which one, but that's another story).

But still I'm an optimist (which is sort of odd, because I'm a pessimist in many other areas) and I really can't see being any other way in a relationship. Would it be better to "round down", to assume that nothing will come of it, to discount whatever pleasure the fledgling relationship brings? It's easy to say that you shouldn't round up or down, just be accurate - but of course you never really know how the other person feels or what's going to happen, so you have to make some assumptions and interpret things according to some mental model.