Why is it advisable to focus the specimen by moving the adjustment knobs away from the slide and not the opposite way?

You always focus by moving the slide away from the microscope because if you focus towards the microscope you will break the slide since you can't see how close it is when you are looking through the eye piece.....it is very easy to break the slides and the focus wheel adjustment is essentially a geared lever and is much stronger than you think. By the time you realize the slide is touching the microscope it is too late...the slide will already be cracked/broken.