When you chop down trees and float them downriver to the sawmill, sometimes they form terrible logjams. The logs get all tangled together and block the entire river. To untangle the mess, you need to find the keylog. This is the one log that is causing the mess. If you can move that log, you'll open up the entire flow again.
So, a keylog is something that is impeding the orderly flow of things. It's causing a break in the system.
On the other hand, a keystone is an engineering concept. The ancient Romans figured out that in order to keep an arch from collapsing, you needed a special shaped stone at the top to equally distribute the load. Arches are incredibly strong structures that can carry enormous weight. To this day you can see Roman arches standing tall.
So, a keystone is what holds everything together. It's the structure that supports your business.
The problem is that they can very easily be confused. When you are trying to make a company more efficient, you can't just look at flowcharts! Sometimes on paper what looks like a keylog is really a keystone. I've seen situations where idiot consultants made decisions just based on flowcharts.
Identifying a keylog and eliminating it is always great. But when you fire a keystone, you only hurt your business.
Make sure you understand (and can identify!) the difference. To learn more about work flow process, click here.