Think of one of your most cherished memories. What do you think determines how you remember it today? You would think that your memory of the experience is determined by how good you felt, and for how long. However, research shows that the duration of an experience is mostly neglected when we think about our past.

Two things influence how you remember an experience: how you felt at the emotional peak of the experience, and how you felt at the end. 

More:
The riddle of experience vs. memory (TED Talk) by Daniel Kahneman
Thinking, Fast and Slow (book) by Daniel Kahneman