More work you do, the more you'll noticed your errors.
Last year while leading A Day of Hope I noticed this "error principle" in our Charity Food Bag Drop. A major part of our donated food collection comes from our Charity Food Bag Drop. We drop off empty paper grocery bags on Saturday to homes in our city, and we return the next day to pick them up filled with food and other items that homes would like to donate for our food distribution. This is an event spread over Friday, Saturday and Sunday. Then it's repeated a second time the next weekend doing the same thing in different neighborhoods of our city.
It's a pretty intense event. Like most events and projects, it starts very small its first year, but grows larger and larger as time goes on. After four years of doing the project, we were delivering grocery bags to over 10,000 homes in our city.
What I found is that every year we found mistakes that we were making (big surprise, right?). However, the mistakes were being found based on the same way we did the event the year before. The year before we hadn't experienced the mistakes and errors. It felt odd because the mistakes felt like they were coming out of no where.
What we realized is that as we delivered more grocery bags to more homes every year, our number of errors and mistakes would enlarge, not because we were making more mistakes, but simply because we were delivering more grocery bags.
Here's an example: Let's say we deliver 1,000 grocery bags to homes. And 5 out of every 1,000 grocery bags has a flyer stapled incorrectly to the bag. So we had five errors. Then the next year we deliver 10,000 grocery bags to homes. Except now instead of 5 bags stapled incorrectly, we now have 50 stapled incorrectly and that can be a real problem. 5 errors can easily slip through the cracks, but 50 is a problem.
When leading projects, remember the more work you do, the more you'll notice errors.