I once attended a scientific conference where several of the speakers were doing research into longevity. Each had a promising area of research. We have learned a lot about aging in recent years and know many of the biochemical changes that take place. There are drugs and other interventions (like calorie restriction) that show promise in slowing, stopping, or even reversing some of those changes. The speakers explained their work and why it had promise, then invited questions (as is standard practice in scientific conferences).
The first question for every speaker was usually the same: Where's your 5-year-old mouse? Mice are commonly used in medical research for many reasons. They are easy to breed and keep, their biochemistry is reasonably similar to humans (and most other mammals), and their life cycle is short and fast. Testing longevity drugs on humans would take decades. Mice only live a year or two. So if someone discovered a drug that could significantly extend human lifetimes, it is likely that it would be tested on mice first. If a drug really was the breakthrough we hope for, pictures of 5-year-old mice would be on news shows and websites everywhere.
None of the researchers was able to show a 5-year-old mouse. Some did have good results with lower animals like flies, some had mice that were measurably healthier in their later months than controls, but no one had the holy grail. But this is not a story of failure: research continues, new things are being tried, and new things are being learned and shared at conferences. My point is that science is successful precisely because everyone knows what the hard questions are and can't duck them.
Contrast science to, say, advertising. A commercial on this year's Superbowl for vitamins touted their benefits by saying “Centrum Silver was part of the recently published landmark study evaluating the long-term benefits of multivitamins.” This statement still appears on their website, verbatim. They can say these things safely knowing that no one will ask the obvious question—so what were the results of the study? Even the website doesn't link to the study, for good reason. The study showed no long-term benefits from multivitamins. But advertisers aren't scientists. They can give their audience carefully crafted, misleading—but totally true—statements while ducking the obvious questions.
Many people think science is about studying lots of facts discovered by people many years ago. That's certainly part of it, but far more important than yesterday's answers is learning what the right questions are.
Advocates for a product or a cause can make a very eloquent case, even if they're wrong. This is because they don't have to face hard questions. A book, a movie, or a TV documentary can all make you believe nonsense because you can't talk back. And if an idea supports our ideology, or benefits us, we are more likely to believe it without questioning, even when we can ask questions. Good scientists know this, and are trained to be most suspicious of things they would like to believe, like the idea that they could live longer.
This habit of being overly credulous or optimistic about things we would like to be true is called confirmation bias. It's another habit of bad poker players that we can take advantage of. They want to call, so they convince themselves that their opponent is bluffing. They want to fold, so they convince themselves that their opponent has the nuts.
Be skeptical. Especially of yourself, and what you want to be true. Don't ever forget to ask yourself the tough questions. Even if you're telling me what I want to hear, I'm going to tell you to shut up and show me the 5-year-old mouse.