Attention, memory and perception
Peak-end rule
People judge an experience mostly by how it felt at its most intense moment and at the end, not by the average of every moment.
Memory isn't a recording. People remember the high or low point and the ending, and largely forget how long it lasted.
Find the moments that matter most in a journey, make the best ones better and the worst ones less bad, and pay attention to how things end: the confirmation, the finished task, even cancelling.
In practice
A tax filing service that ends with a clear summary and a friendly 'you're done' is remembered more kindly than one that ends on a plain receipt.
Common mistake
Ignoring a painful middle because the ending is nice. A peak can be the worst moment, and people remember that too.
Where it comes from
Shown by Daniel Kahneman, Barbara Fredrickson, Charles Schreiber and Donald Redelmeier in 1993, when people preferred a longer cold-water ordeal that ended slightly less cold.