A brief explanation why…
In the original Pac Man (released in October 1980 as an arcade game in Japan), the red ghost Blinky was written to follow behind Pac-Man, Pinky is tasked with getting in front of Pac-Man, Clyde would sometimes behave as Blinky and other times wander off on his own, while Inky the blue ghost was intended to be unpredictable: he might behave as Blinky, Pinky or Clyde.
The ghosts were described in Japanese as having the following character personalities:
Blinky: "Oikake" or "Chaser"
Pinky: "Machibuse" or "Ambusher"
Inky: "Kimagure" or "Fickle"
Clyde: "Otoboke" or "Feigned Ignorance"