In Pokemon, there’s a limit to how many moves your creature can learn. After having 4 attacks, Pidgey’s going to have to forget something so that he can learn Whirlwind.
I’m slightly worried that this appears to have happened to me. Since in the last two weeks I’ve managed to eat on a regular basis my sleeping pattern seems to have gradually deteriorated to the point where I’ll end up lying in bed with the lights off for a good three hours before I eventually dose off, getting two hours of sleep in before hearing the infernal beep of my phone’s alarm. I think I’ve forgotten how to sleep at the expense of eating.
I should probably do something about this.