Because you will focus past ("overshoot") your specimen. (Like using a race car as a shopping cart: it's too fast, and you'll fly past the cereal and never even see it before you realize you need to stop.) Also: you risk crushing the slide and objective against each other (on older or cheaper scopes), and that would be a costly (and embarrassing) mistake.
Because they are the essential micronutrients for the different metabolites of living organisms?
The abrupt breaking of rocks or explosions, fro example an earthquake or Nuclear bomb.
