Today in "math things that probably should have clicked for me sooner but I'm just happy they clicked":
Gram-Schmidt is usually presented as "any finite-dimensional inner product space has an orthonormal basis", which is obviously very neat and useful to know.
However, if you think about it, this also means that every single inner product (on a finite-dimensional vector space) is just the regular Euclidean dot product applied to a different basis! Which is, like, even cooler!
"How do we formally explain why the Euclidean inner product is the 'correct' choice of a canonical inner product that matches our geometric intuition" is a question that's been stewing in my brain for a while, and now I have another good answer! :D