I'm sure I can help make you feel better. Just last year, my first mistake in a really long time... I set up my campaign to go to a list of our clients with an email directing them to a landing page with a form. When someone submits the form, we have an internal email that starts with "Alert" in the subject line so that it can be easily recognized by our inside sales group. That email also prepopulates with some data from SFDC such as contact name, email and company.
So, when I sent the email out to about 25000 of our customers, I picked the alert email to go out instead of the promotional email!
I guess the good news is that the alert email did generate quite a few people letting us know that contacts were no longer at their agency so we were able to clean up our database and add new contacts from them. However, to this day, I still check which email I am picking about 500 times before hitting that send button!