Truth. It is almost the most simple dietary math there is. The more nitrogen in the form of urea, ammonia and other nitrogen containing substances our kidneys eliminate, the more protein we need to eat.

Unfortunately though I don't think the guidelines are very good. Moreover they vary greatly with the activity level. It is a very YMMV kind of thing. The keto calculator says I should get about 100g a day. I hardly ever do. Fortunately I find I have two thermostats (proteinstats?) to guide when I need more protein. One is when I crave a protein shake and sometimes I really, really crave a protein shake. It happens maybe once a month and I can eat as much other food as I want and it will not be enough until I get a ~50g shake which is the lowest calorie thing to have when I need more protein. The other thermostat is when my right calf muscle starts twitching a lot. I find generally that when it twitches, 25g will make it go away.