A friend of mine from many years ago thought she knew what her birthdate was. I'm sure, like most of us, she would have been willing to bet money on it. Then one day a thoughtful friend gave her, as a birthday gift, one of those newspapers that were published on the date of her birth, from the area she was born in. She thought the gift was "so cool". But in checking the accuracy of the paper, she noticed the weather at the time of her birth; "clear and sunny". This didn't square with her mom's account of the day she was born. My friend had been regaled, on more than one occasion, with the story of how she was almost born in the car because it was raining so hard that some of the streets were impassible, making it difficult to get to the hospital. But yet there it was in black and white: "clear and sunny". Her first thought was that this novelty newspaper wasn't what it was advertised to be. So she decided to prove it. But a check of the Farmer's Almanac for that day and area revealed that it was indeed "clear and sunny"; and the National Weather Service agreed with the Almanac. Turns out, the date on her birth certificate was off by seven days, and rather than her parents correcting this when it was discovered, they simply celebrated her birthdays to coincide with the printed document.
The moral of the story? You don't know your date of birth you believe it is the date on your birth certificate. Knowledge and belief are two entirely different things. But sometimes the two are used interchangeably. No big deal, right? It really doesn't significantly impact anything if your real date of birth is a few days different than what you thought it was. But what if you thought (knew) that something you consumed on a regular basis was beneficial to your health, when it was actually harmful to your health. Many people I speak to know that milk and dairy products are good for your health. So it's natural, since they know this to be the case, that when they're given information to the contrary, they dismiss it out-of-hand because they know milk is good for them. In reality, they believe milk is good for them. In reality, milk is not a normal, natural part of an adult human's diet, and does way more harm than good.
So why am I making this distinction between knowing something and believing something? If I asked you, "Is milk good for you?" your ability to hear the reality about dairy products is greatly affected by your answer. If your thinking process is, "I know milk is good for me", you might have a difficult time hearing the facts surrounding this topic. If, however, your position was, "I believe milk is good for me" (same as, "My understanding is that milk is good for me), then you're more likely to be open to hearing information about the topic's facts and fictions. And you'll take at face value "facts" from "authorities" (whether in print or on TV) instead of seeing them as the Gospel truth (remember, although from an authority, my friend's birth certificate was incorrect; no doubt an honest mistake, but a lot of information regarding things like diet and what's good for your health is intentionally misleading).
Needless to say, being open-minded, especially about issues dealing with your health, is in your best interest. And one of the best ways to be open-minded is to realize that many of the things you know to be true, you instead believe to be true and it's in your best interest to acknowledge that there's a difference. Remember, "What can do you the most harm is what you know, that just ain't so."
more in-depth look at the definition of knowledge, watch this ten