For my first edition Camel, O'Reilly printed 10,000 copies, expecting that this would be the inventory for an entire year.

They sold out in the first month!

I think we hit about 30,000 copies in that first year, but that's a long time ago, so I might be mistaken.

On the other hand, 4000 copies would be more copies than some other books that you've definitely heard of had ever sold. So, 4000 is not an unreasonable number for a "fresh out of the gate" author, even if we've all heard of him.