Following on from this I decided to put my groceries on the belt at random -- took a little effort but it was amusing to watch my internal reactions to doing this.
If this stuff is really obsessive you could try the behaviour modification technique: look at the torn chair and say out loud `I need to repair that rip'. Count how many times you have to say it until your mind gets bored and wanders onto something else. Repeat that many times as often as needed.
Or try a meditation course -- they have some good insights into thoughts and how they get to us.