Expressers underestimated how positive recipients would feel, overestimated how awkward they would feel, and underestimated how surprised they would be.
How it was done
Experiments in which people wrote gratitude letters and predicted the recipient’s reaction, with those predictions compared against what recipients actually reported.
What it means
The mechanism is a mismatch in what each side is attending to. Expressers evaluate themselves on competence — was that well put, did it sound strange. Recipients are not assessing the writing. They are registering warmth.
Because the sender is grading a performance nobody else is watching, the anticipated cost is inflated and the anticipated benefit is discounted.
It generalises past thank-you notes to most of the small unprompted contact people talk themselves out of.