I know this can be a touchy subject, but honestly, it shouldn’t be surprising.

It’s just basic thermodynamics.

The energy (calories) you take in has to go somewhere. Some of it gets used for daily activity, but if you take in more than you burn, your body has to store the extra—it doesn’t have any other way to deal with it.

At the end of the day, it really is just a matter of calories in vs. calories out.

Exercise just helps burn more of your excess energy so that it doesn’t get converted into (weight) storage.

https://en.m.wikipedia.org/wiki/Laws_of_thermodynamics

Thermodynamics only apply to closed systems. Your body can easily expel unprocessed calories/sugar in urine and feces (hence diabetics historically being diagnosed by their characteristically sweet urine).

Whether it's more likely than the average human body to do so, to process them for immediate energy, or to process them for longer term storage in conjunction with how it benchmarks your hunger and satiation signals is colloquially known as your "metabolism".

Want to tell me next how the laws of mechanical engineering conclusively prove that no one human being can be stronger than another, since we all weigh the same?

Yeah it's odd we needed a whole article for this. "You can't out exercise a bad diet" has always been true outside of the most extreme cases (competitive athletes).

Maybe it shouldn't be surprising, but without the knowledge, the opposite of the thing can be explained the same as the thing itself. For example, "The energy you take in has to go somewhere", but I also poop everyday, so maybe I just poop out the unnecessary calories? I know it works for water soluble vitamins for example.

Hindsight is 20/20 in this case. It's nice that the explanation is not complicated ("calories in, calories out"), but many other simple things have been thought of as true, only to be put on their head by science. I welcome the scientific confirmation, and I hold that the path to knowledge it's not straightforward at all.