you've got to crack a few eggs to make an omelette
Sometimes, you have to do unpleasant things in order to complete a task or meet a goal. Your students clearly don't respect you. I know you don't want to yell at them, but you've got to crack a few eggs to make an omelette.If I don't cut people's salaries, the company is going to go bankrupt. It's unfortunate, but you've got to crack a few eggs to make an omelette.
something that you say which means it is difficult to achieve something important without causing any unpleasant effects Twenty jobs will have to be cut if the company's going to be made more efficient. But you can't make an omelette without breaking eggs.