It also helps to hold the hair in a fist. Like if you take sections and you start at the bottom, hold the section in your left (or right) fist about 3 inches from the bottom and brush. Don't be super rough.. don't be too soft either.. it needs to be like you are raking leaves from the ground. Once all the tangles are out of those 3 inches, hold another 3 inches upward (6 inches should be below your hand) and brush the knots out of those 6 inches. Then however many inches of mane you have left, release the section and brush from the top down to the bottom. I like to put my hand under it so I get all the hairs. Then hold the section up, brush from the base to the tips.
Some hair WILL pull out just like humans :P But don't just brush without removing the knots or you will give your horse a very ratty mane (lots of breakage or hairs that have been frayed etc.) and it'll be stringy and damaged.
Tip: spray the mane in a very slow but large mist so it isn't DAMP but it's lightly covered, and then spray your brush and shake it then start brushing. Less hair will be pulled out.
Another tip: The longer you leave the de-tangler IN, the easier it will be to brush (so I've noticed.)
Third tip: You can also use a regular comb to get the knots out, THEN use a brush to fluff as we wrote before.
Good luck :)