A picture is worth a thousand words. The above photograph, tweeted by @stuartice, illustrates why we need to think about the wider system when solving problems. This is especially true when, as in this case, the wider system involves sentient actors who may not share our goals.
Similar effects can be seen in any situation in which decision-makers are trying to save people from themselves. If we don’t consider the reactions stakeholders will have to a decision, we’re bound to make the wrong one.