thats based on the concept that you can lower more weight than you can lift?
Yes, that's true, but it has more to do with overload principles. If you consider a sprinter who trains with a parachute, his body is being conditioned to extra resistance. When the chute is removed, they will typically run faster or with more efficiency now the load is removed. Just like doing chins with a weighted vest for a few weeks. Once the vest is removed, you should be able to do more chin ups.
From a weight training perspective, someones 1RM might have become stagnant or not increased proportionally in one lift compared to other body parts. For those that rarely train with lower reps, when you get to 1-3RM's, typically the muscle and the mind are not conditioned to such sudden and extreme weights. If you aren't use to that kind of load, you won't be moving it far.
Enter, Negatives. They are usually performed with weights about 10% over your 1RM. Let's use bench press as an example; Ideally, you need 3 spotters - one on each end of the bar and one in the middle. Load the bar up 10% over your predetermined 1RM and have all three assistants help un-rack the bar. The bloke in the middle never lets go of the bar as he helps giude it down. The other two get ready to catch if it goes pear-shaped. From lockout, you begin lowering the bar. After about 1/2 way, it will feel like your just trying to slow it down. At the bottom, the spotters lift the weight back to the top and you go again.
Essentially, what you are doing is training the muscle and your mind to handle weights heavier than what you're typically use to. When done regularly, the next time you try your 1RM, you will be comfortable with the weight and you should find it that little bit easier. Hell, you might have just managed to boost your 1RM a couple of KG's.
Just remember, form is absolutely critical here. You are working with some serious weights on compound lifts. When done correctly, good gains can be made, without injuries.