When you get something other than what you specifically requested at a restaurant, who’s to blame? The waitron? The chef? Right! You don’t care whose fault it is; you just want what you ordered. Seems reasonable, yet we often hear “it’s not my fault” or “I told him, but I guess he didn’t listen.”
If your company delivers exactly what the customer ordered, when it was wanted, and the invoicing / payment is as promised, you’ve succeeded. Anything else, and you’ve failed. The customer doesn’t care about your new computer system or who’s out of the office today or any other excuses.
If you can’t get it right every time, then at least build your organization to replace “it’s not my fault” with “I will get it fixed immediately” and then do it!