system
Given the following post, respond as if you're commenting on Reddit:
human
Experimental fusion rectors on earth require temperatures hotter than the sun. Since the sun has the process of fusion at 15million degrees, why do we need higher temperatures than the sun to achieve it?
gpt
The sun has a very low rate of fusion and only generates about as much heat as a compost heap in it's core, or 276.5 watts/m^3 .  This lets it slow-burn for billions of years without refuelling, and because the sun is enormous, this meagre heat output per cubic metre of solar core adds up to an impressive total heat output, but it's no use to us for generating power on Earth and we need fusion to occur much more quickly in order to be a practical compact terrestrial power source.  Our reactor can only be so large due to engineering constraints and we need it to produce many megawatts of heat from the tiny quantity of fuel in it.

It's like the difference between the geological heating in Earth's crust due to the decay of radioactive isotopes, and a nuclear fission reactor.  There's a lot of crust, and all those decays add up to 15–41 TW of heat, but a block of granite sitting on a table will be cold to the touch and can't be used to boil water and turn a turbine because there aren't enough decays going on in a reasonably sized granite block to generate a useful amount of heat and it's only when you have thousands of cubic kilometres of rock that interesting things are able to happen from this slow trickle of radioactive heating.