I’m getting older so maybe this bias is more relevant for me than I would like it to be. The positivity effect means that: “Older adults favor positive over negative information in their memories.”
Why would that be? Maybe we need the drama when we’re young and the consolation once we’ve had enough. Life’s complicated. It helps to remember that you did what you had to do, even when you should have done something different.
What has UX got to do with this? Always put usability first. There might be a tight budget, dreadful technical contraints and an impossible deadline, but álways make sure that the user can complete the task.
Because a task that has failed will be a failure forever. But a task that was completed, even if it was a struggle, can be remembered more positive than it actually was. People won’t forget failures, but they are willing to forget mistakes.