Systems are always more complex than we think of them. Side effects are not only less predictable than we imagine, they are (all too often) less predictable than we can imagine. A parable in this regard is a little-known side effect of the tremendously successful Star Wars movie franchise: children dying.
By coincidence, a fireman dressed in full rescue garb, including black oxygen mask and helmet to ward off smoke inhalation, resembles Darth Vader, and other dark lords of the evil empire. Children trapped in a fire and at peril of their lives, turn and run from their rescuers; sometimes indeed (though blessedly rarely), fleeing to their deaths.
The lessons are two: If you have children, acquaint them with how a fireman looks when he is about a dangerous rescue. Point out that in a fire, an "evil looking" spaceman is a friend, come to help!
And (with lesser urgency) if you put together systems, respect the idea that any small, innocuous-seeming new element can have unexpected side effects. Be alert for new surprises with any change. After all, what could be more harmless to children than a well-made escapist space opera, like the Star Wars saga, source of enrichment and harmless entertainment for millions?
