Small mistakes are easy to catch and fix. A tax collector will sooner notice one person not filing papers for two jobs than a big corporation messing their taxes.
Small mistakes are not unimportant. But if we only focus on them, we miss the big ones, which hurt us in the end much more.
Spending time collecting another 20 Euros from a person will probably leave you with a loss in the end. But spending time and getting 20 millions will be most worth it.
Do not get stuck in the small mistakes.