Why NOT to use existing music and clips, EVEN PAID and LEGAL. Does “FAIR USE” apply on YouTube?

It can be discouraging when you get permission to use a song, pay for a license, and STILL lose monetization of your video due to a large company claiming it. And it’s even worse (in my opinion) when you use clips under FAIR USE – as part of education or parody – and lose 100% of your video’s revenue.