Security through (by) obscurity is where we try to protect an asset by hiding it. Anyone who has ever played the game Capture the Flag knows that a motivated opponent will eventually find the flag. If there were no other deterrents in place, the opponent will scour the playing area and find the flag. If hiding an asset (the flag) doesn’t work for that simple game, it doesn’t work for information security.
However, Capture the Flag doesn’t just involve hiding the flag. In all variations of the game, all teams have attackers. Therefore, part of the deterrent is acting quicker than your opposition. In a lot of variants, each side also has defenders who have some ability to discourage or thwart attackers. Even if the particular variant doesn’t have the concept of defenders, a team can be sneaky. It can overload one side, trying to trick the opposing forces that the flag is hidden over on that side. Or some of the attackers could mock act in dismay when an opposing team heads into the wrong area of the playing area, leading that team to think they are close to the flag when they aren’t. In other words, there are always additional countermeasures.
The problem in information security with a strategy of security through obscurity alone is we are making the assumption that we are smarter than any adversary with plenty of time and opportunity on his or her hands. We don’t. Therefore, we need to have the other appropriate countermeasures (controls) in order to protect our assets. There’s nothing wrong with making an asset harder to find (obscuring it). However, that can’t be our only mechanism of protection.