Positivity Effect

I lead bicycle rides around middle Tennessee.  Often, I have a ride started and not too far into the route the grumbling starts.  I hear, "I thought you said this route was flat."

Well, I thought it was.  I honestly didn't remember all the hills, but sure enough.  We got hills.  My comrades don't except my excuse of "these hills weren't here the last time I rode it."  Finally, I just tell them, "I'm old.  I no longer have space in my database to remember the bad things.  So I triage my memories.  Good stays; bad is out."

I have recently learned, while studying cognitive biases and why people believe idiotic things, that I am hardly alone in my bias.  It even has a name "Positivity Effect."  Wikipedia explains it  as follows:

The term positivity effect refers to age differences in emotional attention and memory. Studies have found that older adults are more likely than younger adults to pay attention to positive than negative stimuli. As people get older, they experience fewer negative emotions and they tend to look to the past in a positive light.  In addition, compared with younger adults' memories, older adults' memories are more likely to consist of positive than negative information and more likely to be distorted in a positive direction.  One theory of the positivity effect in older adults' memories is that it is produced by cognitive control mechanisms that improve and decrease negative information due to older adults' greater focus on emotional regulation. 

 The positivity effect probably also explain why most older adults remember their childhood as being simple and pleasant.