Attention, memory and perception
Negativity bias
Bad experiences stick in people's minds more strongly than good ones of the same size.
One failed payment can outweigh twenty smooth ones. People notice, remember and talk about negative events more than positive ones.
That's a reason to put real effort into error states, edge cases and recovery. A good apology and a quick fix after something goes wrong can save the relationship.
In practice
An app that explains plainly what went wrong, what happened to the person's data and what to do next keeps trust that a generic error message would lose.
Common mistake
Treating errors and empty states as an afterthought. They're often the moments people remember most.
Where it comes from
Summarised by Roy Baumeister and colleagues in Bad Is Stronger Than Good (2001), and by Paul Rozin and Edward Royzman the same year.