Why drop-in visits are not allowed:

I’m no different than your doctor, dentist or lawyer in that I’m always in the middle of doing something and if this something is interrupted, it usually costs me money. My train of thought is interrupted or something I’m in the middle of gluing becomes ruined. No one likes to be interrupted in the middle of something they are concentrating on.

I tried having an open door policy years ago when I first started and I quickly realized that that it was putting me out of business. I’m a social person, I love to talk and am easily distracted. So this rule is as much for me as anyone else.