The thing is landing a man on the moon took dedicating a few percent GDP of the most advanced nation in the world for a decade and scientists poached from the next n countries after the war: perhaps your X isn’t actually the harder problem.
Perhaps X just doesn't have enough geopolitical relevance to fund it with ridiculous amounts of taxpayer money.
If a problem that ought to be simple is actually hard, it's very likely that it's because whoever's making decisions doesn't want to pay for it.
Simple example: queues. It's a mathematically solvable problem but someone somewhere will think that hiring enough people to provide perfect service is too expensive and they're better off making people wait in line instead.