I've often wondered why there is so much misinformation around the topic of the reasons that very massive main sequence stars are so luminous. It even shows up in books, but if we restrict to seemingly reliable internet sites, I'll bet that in 10 google hits of sites that offer an explanation, you'll find at least seven that claim massive stars are more luminous because their cores are hotter, and maybe as many as five that add it is because the pressure in the core is higher. Those are both wrong explanations, the first for subtle reasons, and the second for appallingly blatant reasons. The blatant reason that it's not because of the high pressure is that massive star cores have lower pressures than low-mass stars, for the simple reason that their high mass allows the core to reach fusion temperatures with much less compression and much lower pressure. At least higher core temperatures is actually true, but the subtler reason why that is not the explanation for the high luminosity is that it reverses the correct logic: the higher temperature core is because of the higher luminosity, not the other way around. So why is this wrong so many places?