Dear Richard,
Once upon a time in ancient China, a merchant was hard-selling his fighting gears in a market. He brought out his spears and said, 'Here are the sharpest spears on earth. They are made of the hardest metal and can cut through anything without losing their sharpness.' He attracted a big crowd of people; some of them were convinced by his words and brought the spears.
Ten minutes later, the man brought out his shields and said, 'Here are the best shields that you can ever have. They are made of the strongest protection material and nothing can cut them through.' Again, he attracted another big crowd of people and sold some of his shields.
A man who was standing there for a while questioned the merchant, 'If your sharpest spears attack your best shields, what will happen?' The merchant, of course, couldn't provide a good answer, as he contradicted himself severely.
Richard, when listening to others, they could have beautiful words and attractive presentation to make you believe. It is important to think thoroughly. You may find some contradictions, spears against shields, inside their speech.
With love, Dad