Headphone stereo fails because head filtering is missing or double-applied.

Evidence

Normal stereo signals do not reproduce correctly on headphones, and binaural recordings do not reproduce correctly on normal stereo equipment. This is because in the former, the effect of the head is removed from the listening environment, whereas in the latter, the effect of the head is applied twice, once in the recording and once in the listening. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2251

Categorization

• XREF: Connects to the reader’s own listening experience of headphones versus speakers — a practical listening-illumination point.
• CANDY: A tidy elevator-explanation: binaural on speakers means your head gets applied twice.