Usually we don’t get tripped up by difficult, hard to anticipate mistakes.  No, we usually stumble over things that could have been avoided.

Make a habit of this.   After you’ve done something (completed a math problem; painted a door; written a letter; paid the bills, etc.) take a step back and look at your work.

Have you missed anything?   Do the numbers seem to add up?

This type of double checking will prevent these pesky, easy to avoid mistakes.