Why??

How come I can remember nonsense from over 20 years ago such as the quadratic equation, or the table of trig exact values (none of which I have used in that time), but I keep getting the boys names mixed up? It got right up my nose when my mother used to call me by my brothers name when we were lads. In my defense, I've now got 3 born four and a half years apart, whereas she had 2 born 5 years apart. Surely she could have got it right more often? Nevertheless, I keep getting them mixed up - even the little white one. It really can't be that hard, can it?