It's so simple. It's so incredibly, impossibly simple. I liked Feynman's explanation so much that I converted it into flowchart form:
Using this unassuming little method is like following a compass when lost in the wilderness. Despite constant opportunities to veer off course, science keeps you on the right track by forcing your assumptions to adhere to objective reality.
Each step of the process is crucial. If you don't make any guesses, you live in a world devoid of any truth claims. If you don't make predictions, your truth claims are useless. If you don't test those predictions, you'll never know if they're wrong. And if they're wrong but you keep them anyway instead of starting afresh, you'll be operating on potentially harmful false assumptions—and any assumptions built on top of them will probably be false as well.
It's such a remarkably simple heuristic, yet it seems so hard to instill into people as a fundamental value. Why is that? Maybe it's because it seems cold and harsh to unceremoniously toss our cherished ideas out the window when they turn out to be wrong. It's often easier to just go on believing what you've always believed, and sometimes false beliefs just appeal to us more than the truth.
This is where a solid science education ought to come in, but things often go wrong at some point along the way. When I was in grade school, we learned about the scientific method and even used it to do experiments in class. But we were never really shown the deep significance behind the process—how it allows fields like aeronautics and genetics to flourish in just a few decades, while astrology and faith healing spin fruitlessly in circles for millennia. This basic system, carefully honed through advancements like double-blinding, significance testing, peer review and replication, ensures that the map of our knowledge matches the territory of reality. And once we can easily navigate the known world, we can set out for parts unknown, on a voyage to fill in the farthest reaches of the map.