What's the thing a teacher can NEVER forget?

This day will be unforgettable in my whole carrier. As it is the case on every Sunday,I got my stuff ready & I had my breakfast & headed to the car where my father was waiting. After 40 minutes of driving we made it to the other city. By the time I reached school I just reached out for something vital that a teacher is meaningless without & that he could never forget...Something I hoped my pupils would not notice, but that's hard to wish for...At the end of the first class a clever student of mine asked me : "Teacher! where's your school bag?" hehehehe such an awkward situation...The only answer she got from me was: " Have you ever seen a teacher without his school bag?" She said: "NO" well then I said :" Then DON'T believe it..."
HAHAHA...
Expect the Unexpected....