We are all human and sometimes do things subconsciously. You do something 99 times then the 100th time it does not work! We all get it and do it.
A customer came in today with some ink cartridges and said they would not print. These cartridges were some of the most popular ones we sell the failure rate is less than 0.5%.Nothing is perfect. They had purchased these cartridges from me for years and never had a problem, I was intrigued. On a lot of ink cartridges you have to peel off a strip of film that covers a hole in the cartridge. In use the hole allows air into the cartridges and ink to flow out. The customer had removed the big red plastic bung off the bottom of the cartridge but forgotten to remove the tear of film on top. Hence the cartridges would not allow ink to follow and the printer printed nothing.
On examining the cartridges I noticed this error and as tactfully as possible pointed this out to my customer. Their reaction was “I HAVE BEEN HUMAN!!” sorry to have bothered you.
The point of this is that if something we normally do does not work, take a break. Try again from the start and in 99% of cases the issue goes away. I have done this, occasionally it is a faulty cartridge (less than 1.5%), and we simply supply a free replacement with an apology.
We live and learn!!!