Daring Fireball: “Once software starts down this path of guessing what it is the user is trying to do, and then doing something special based on that guess, it must guess correctly nearly every time, because the times when it guesses wrong are so annoying that they far outweigh the extra convenience of the times when it guesses right.”

It’s easy to start to concoct ideas about clever things that your software could automatically do, but this is a useful rule of thumb: If you can’t get it right almost all of the time, don’t. Focus on making it easy for users to know exactly what will happen instead.