I think it's the reason we have kids. So we can get to daycare, ring the bell, and hear through the door, "Mommy!" And then listen to the excited footsteps running to the door.
It's particularly special for me because I waited so long to hear the word; Theo was well over 2 when he learned it. Most moms get to hear it (or some version of it) when their children are 1, even if they're not saying anything else.
I'm not complaining. Waiting only heightened my anticpation, and sweetened the music that it is when I do hear it now.