I've met a lot of people who don't seem to understand this important concept from epistemology, which is the philosophy of knowledge.

To demonstrate the concept of "non-falsifiability" I will now produce a short fictitious dialog between a made up Scientist, S, and a Religionist, R.

Topic: how old is the earth? Is it 6,000 years old or more than 4 billion years old?

S: The earth must be more than 4 billion years old, because I found these rocks. These rocks have isotopes in them and they definitely look like they've been around for more than 4 billion years. If the rocks are really old, then the earth must be really old too.

R: No. The is only 6,000 years old, because the holy Bible has a list of human descendants from Adam, the first man, to Jesus, who we know was born in 4 BC. If you count it all up, you can find the exact year that the earth was created, as described in Genesis 1, and it's about 6,000 years.

S: But these rocks.... They're really old...

R: God must have created those rocks with the isotopes already set up in the correct ratios to look like they are 4 billion years old, when He separated the firmament from the heavens 6,000 years ago.

S: But how could God create rocks with different isotopes? When minerals solidify from molten lava, lead isotopes naturally form in this ratio. (I don't actually know how initial lead composition was established for this)

R: God is omnipotent! Any miracle is within his grasp.

S: But why would God want to make the earth appear to be much older than it really is? What purpose does it serve?

R: I do not pretend to understand the ways of God.