Two over 10 years doesn't seem like that much, but I guess even one is too many. What do you see as your life lesson here though?

Sorry for the delay:

In both time I knew it was happening, but I was too busy to fix it.

It almost happened again - I pulled the employee off the job, made him document everything, and put a team of people back in. He was banned from the job.

Kept both him and the customer.