Biggest Fitness Myths

Oh, so many fitness myths out there. How do you muddle through all the info on fitness to find what is worth it and what is worthLESS.
The myth that is making me crazy is:
"Muscle weighs more than fat." HUH! Lets think about this. If you have 5lbs of feathers or a 5lb block, they both weigh 5lbs. The difference is in the space it takes up. It would take a room full of feathers to equal 5lbs, but a block is compact, dense, and takes up very little space. 5lbs of fat takes up more space than 5lbs of compact, dense muscle, but they both weigh the same. 5lbs of fat is not as metabolically active as 5lbs of muscle either, but they both weigh 5lbs.
Get it?? Lets put this myth to rest and let common sense take over.