There's a phase that small kids go through, when they've just learned how to talk enough to have something sembling an intelligent, intellectual argument. They like to practice this by wanting to disagree about anything - mainly general statements that were not 100% perfectly waterproof. If you tell a 4-year-old that bananas are green when they're raw, and they turn yellow when they're ripe, there's a good chance that they'll give you that "well that can't be right" frown, and start to argue. Surely not all bananas that are yellow are always ripe.

Unfortunately humouring them about these arguments is very important for their development and a great opportunity to teach them more about how the world works, so you'll sometimes end up arguing about things like these, and every single time when you explain that's not how something works, they'll come up with another argument starting with "but what if-", until you are forced to admit that yes, if someone did for some reason take one single green banana, spray-paint it yellow and then expertly textured it to look just like a ripe banana, and then break into a grocery store in the middle of the night to slip that one painted banana into the display of ripe, edible bananas, then that one specific yellow banana would not be ripe and ready to eat.

As far as the child is concerned, this means that your entire initial statement was false, and you were wrong and they were right. Their need to be correct about something has been satisfied. Fortunately, most children grow out of this phase eventually.

The ones that manage to survive into adulthood without growing out of it end up on Twitter.