Do designers know how good their games are?

How well do designers understand how good their games are, or how well they will sell (which is two somewhat different things)?Reiner Knizia (over 200 games published) recently said that his game Pickomino has quite surprised him. Pickomino is a dice game with scoring tiles that's fairly simple, but has become a big seller.In my own case, 25 or so years ago, after I had had some games published,