Moss grows where moisture hangs around longest, and in most forests that is the north side because it gets less direct sun. Your buddy is half right that it is about moisture, but direction drives the moisture. The catch is it only works when you have enough tree cover to keep the shade uneven. Out in the open or in a spot where wind and fog hit one side harder, north means nothing. I have tested this on and off for years in western Washington and it held up maybe 7 times out of 10 on big old trunks, but on smaller trees it was a coin flip. Pacific Northwest is actually a decent place for it since we get so much fog, but watch for creeks and low spots because those throw it off. So the trick is real, just not a guarantee, and checking more than one tree is the only way to trust it.

Disagree with the whole "just buy better soap" take, because technique really does matter more than people admit. If you're not rinsing with hot enough water or you're stacking wet dishes so they air dry in a puddle, even good soap leaves spots and haze. Try washing one glass with that same cheap lemon stuff but rinse it under running hot water for a solid 20 seconds and dry it with a clean towel right away. I bet it comes out clear, which means the real issue was how you rinsed, not the $1.25 price tag. People love blaming the product because it's easier than admitting their method is lazy, but a film that only shows up under your kitchen light is classic soap residue from not rinsing enough. So what happens if you test that one glass tonight, does it still look cloudy?