Alzheimer's?

Every once in a while I catch myself questioning the spelling of some easy word. Not a good thing considering it's important to what I do for a living. I don't think I'm letting misspelled words get by, but I do find myself reaching for the dictionary more often for reassurance (I just needed reassurance for "reassurance"). Today the word "listen" tripped me up. It just looked wrong to me. There's a "t" in the middle?! Really?! Why?! That doesn't make any sense at all! Maybe the English language is one of those things that retains its mystery even after you think you've got a handle on it. Or should that have been "gotten"? See what I mean? It never ends.