Now I understand, thank you. I was confused with what Chris told me about Mora Swedish knives:

"[...] Still, they are one of the few carbon steel knives with sufficient Rockwell to produce sparks with natural stones; a minor, but relevant skill and firemaking option. If you get one, lightly file the spine. As new, flints tend to skip along the slick surface."

"[...] The carbon Moras' high R enables natural flint sparking. The flint ignites the carbon molecules from the blade material. Anything softer than 58-60 and the flint merely gouges the material. Moras have this high R in the blade, and a relatively soft tang. You will eventually bend one, or even get one with a few degrees 'prebent.' They bend back easily."