I caught your fern with its frond in the fertiliser again.
Madness string 355
'Believe' is not the right word here. If you believe in chairs, it means you think that they exist. If he doesn't believe in chairs he's a nutter, if he doesn't worship chairs he's a normal person. The only other interpretation is that he doesn't have confidence in chairs, like maybe he fell out of one too many, which would also be very strange.