I'd flip that and decide that there is no algorithm that exists and is documented that you can't implement yourself, for amusement and educational value or, given time and the will, more than that. Just making that decision has value for you even if you don't actually do it terribly often.

Same as you can design a cpu in HDL and flash it to an FPGA. (The "Nand to Tetris" course seems popular) Same as you can write an OS. Same as you can write a compiler and/or interpreter.

Believing these things (and they're actually true!) gets us all away from learned helplessness. There's enough of that when it comes to actual silicone...

Nobody understands it all. _You_ understand as much of it as you choose, in the direction that takes you, as deep as you want to go. It's just work, a lot of it, but no more than that.