Why did a pixel with an excellent color appear on the screen of mbp 15 2012 on a black background?

Question

Monitors

Why did a pixel with an excellent color appear on the screen of mbp 15 2012 on a black background? It is slightly different from black, if you move a cotton swab, another one appears, and there is still such a feeling as if there is some kind of protrusion along the pixel, and I feel it with a wand

Answer 1

Classic dead pixel. It happens.