How small is small enough

Here is the test. Picture the worst day you have had in the last two months. The one where you got four hours of sleep and everything went wrong.

Could you have done it on that day, without heroics? If yes, that is your floor. If you had to imagine yourself being slightly better than you actually are, it is still a target and it will break.

Almost everybody sets it too high on the first attempt. If you find yourself thinking that it is too small to be worth anything, that is usually the sign that you have got it about right.