Because I will forget!
My little Bryce is about as smart as they come - maybe I'm bias! He can add now...only took me going over it a couple of times with him and he caught on instantly! He can add any combination of the number 1-4. He can subtract sometimes, if I put it in "apples" : example, you have 2 apples you subtract 1. He can add one to any number pretty much, he's gotten that one down pat! But every now and then I'll catch him on a good day and he has been known to add 3+8 or 5+7. It may take him a minute, but he gets it! He's just so brilliant and I didnt' want to forget what he can do at age 4!