Sysadmins are a superstitious bunch. Even when we know better. Unfortunately, we've each had one of those experiences that causes us to wear that tired, 15-year old T-shirt every 3rd Thursday after a blue moon. Because if we don't, the mail server might crash. It's happened. At least twice.
We're superstitious enough that it is embedded within our culture in some way shape or form. Usually, a policy is implemented that firmly institutes that superstition. It may be written or unwritten, but it's there for a reason. For me, there is never any maintenance, upgrades, or system shutdowns prior to any major holiday or just before the person who would do the work goes on vacation. Too many times I've been bitten in that scenario and as a result, my superstition has become policy. Even with proper planning, somehow, some way, the universe wreaks havoc on my weekend if I don't burn an offering to the switch rack or sacrifice a stuffed Tux on that 10-year old Windows 2000 server lurking in the dark corner of the data center.
I feel a blue moon coming...