If you don't get his explanation, think of it like this:
Think of the electricity water. FETs are like the dam that regulates the flow of the water. Stacking FETs opens up more gates, and allows the water to flow more freely. Some motors work so hard that they need the flow to be strong to make it work.
If you have a really high metabolism but you can't eat very quickly, you're going to die pretty much. A high amp draw motor will demand a lot of amps, but the FETs won't allow that much because it only allows a certain amount of amps.
Yeah I am really tired, so that probably doesn't make sense
