Well on my first job we had to integrate payment gateways in client apps for online payment. On my second week in office I published an app on the play store with payment gateway credentials for a different client cause they were there as default values. So the money for one client would go to the other. Nobody noticed it for two weeks and when they did, I thought I had just lost my job and also I would now have to pay all the losses out of my pocket but fortunately I didn't have to cause no transactions​ had yet been made. After that I always checked my integrations atleast five times before publishing. The incident scared the shit out of me but taught me the value of developer responsibility.