The Stairs

Lily warned me not to go down to the basement.
But I needed something from down there.
We live on four, so I went down the five flights of stairs and…
Locked. Forgot the key.
So, I went back up six flights of stairs and…
Six?
If I went up six, I should be on…
Wait. Hold on.
I went back down again, down five flights of stairs, and stood at the basement door.
Then I carefully counted each flight of stairs up.
Six.
“Somethings wrong,” I said.
“I told you not to go down to the basement,” muttered Lily.