How can money go to four decimal places?

But with bitcoin there is really no complication because the system actually pays in fractions. With the money used in FX there is no fractions, you can’t physically hold it.

So I was very surprised to see nowhere really going to detail about why four decimals is happening and why it’s possible.

To me that’s the first thing I need to know as a beginner because we spend our whole life with money in two decimal places.