Expectations

Why do we feel bad when things don't happen the way we planned? Is it because we have a kept unrealistic expectations? or is it because people, on whom you base your expectations, just screw up? Or is it because we always want things to be perfect or close to it atleast, which is a unrealistic expectation, coz nothing can be perfect! Or can it be? So, should we keep expectations? Not meeting them leads to dissatisfaction, pain, agony, depression. And meeting them leads to exactly the opposite of what I just typed. But is it worth it? Putting ourselves into a situation where the probability of failure and success is exactly the same - is it worth it? What if we don't keep any expectations? Every time something works out, it will be a moral victory. If it doesn't, well, we couldn't care less! We didn't bother. But keeping expectations, 'good' expectations, is heartening, gives you something to look forward to, something to dream about, something to wait for, coz the sheer fulfillment of those expectations is blissful. And what if our expectations are very realistic, hardly out of the ordinary, and still aren't fulfilled, for reasons that we cannot control or influence?

So, is there a trade-off? What is the trade-off?