Somewhat related: I've always enjoyed that the matrix multiplication algorithms with the best theoretical time complexity, are completely impractical for use on real-world matrix multiplication problems.

Wikipedia describes why people use the Strassen algorithm in real-world implementations, despite its inferior asymptotic time complexity [0] :

> unlike the Strassen algorithm, it is not used in practice because it only provides an advantage for matrices so large that they cannot be processed by modern hardware.

[0] https://en.wikipedia.org/wiki/Coppersmith%E2%80%93Winograd_a...