Here's the thing that customers, managers, and less experienced developers all have in common: they understand that no one thing is difficult. But they don't take into account that managing the complexity between a thousand, or a hundred thousand, or a million rules is very, very difficult.

That's why you hire more experienced developers: they're more experienced, not at things like cache invalidation (sure, just nuke your entire cache anytime anything changes! easy!), but at managing complexity.

Which is difficult.

That's why I try to keep my mouth shut about how somebody should "just do this, it'd be so easy, why are they dumb?"