Sure, "it's more complicated". But the most basic, predominate mechanism is that you're literally burning carbon and exhaling CO2. Only from that realization can you start to identify and answer more sophisticated questions, including the exceptions.
My point is that you can get an incredible amount of mileage from the most basic principles taught in school. Which is literally the point of a basic education. But people tend to emphasize "don't believe everything you learn in school" rather than "most of what you're taught in school are foundational truths to your environment that can have immense utility in your day-to-day life." If you focus on the former rather than the latter, you won't get into the habit of learning how to apply your knowledge. And if you're not well practiced at application--which is a life-long endeavor for even the most basic rules--then superficially that knowledge tends to seem useless.
I never studied computer science in college--I was already writing Perl and JavaScript when I entered a 101 course which was teaching Pascal, and I dropped it the next week. But I did end up learning--and still learn--the theory and its application. I often hear computer science graduates lament that they never actually need to apply what they learned in school in their professional lives. Well, "need" and "can" are two different things and it's a choice you make. Failure to rigorously apply even basic principles is a big reason, IME, why so much software is utter crap. Do you need to consider algorithmic complexity for every little script you write? Yes! Not because it necessarily matters to the performance of the script, per se, but because the script will be part of a larger data processing system, and the way it fits into and shapes that system can and often will effect algorithmic efficiency down the line.
It's a useful skill to apply first principles to everything you encounter in life. Not just scientific principles, but moral and emotional principles, too.