Next I put together the procedures for manipulating the pieces: pick a tile, flip it, rotate it. But the playfield filled up in 20 seconds flat. Also, once you’d filled a line, it was kind of dead, so why keep it on the screen? So I made each full line disappear, which was key. I was a pretty good programmer and it took me about three weeks to get something controllable on screen. I pretended I was debugging my program, but in truth I just couldn’t stop playing it. When other people tried it, they couldn’t, either. It was so abstract – that was its great quality. It appealed to everybody.