[mjp]

A complex system that works is invariably found to have evolved from a simple system that worked. The inverse proposition also appears to be true: A complex system designed from scratch never works and cannot be made to work. You have to start over, beginning with a working simple system. --John Gall

Also:

1)systems tend to grow, and as they grow, they encroach
2)systems display antics
3)complicated systems produce unexpected outcomes
4)the total behavior of large systems cannot be predicted
5)complex systems tends to oppose their own proper function
6)systems get in the way and the system always kick back

[dirtboy]

Also, abject paranoia should be the foremost guiding principle for systems development, operation and administration.