"Forever" unless the knowledge is out of date, or you don't use it and forget, or until Alzheimer's or some other dementia happens and everything disappears (or until your death, I suppose, but gold also tends to change hands around that time).
So that's a no, because you didn't overanalyze you're response to that question, leading to me having to do it for you and therefore failing your implied social contract.
Do you always succumb to the need to publicly police people? The other person just voiced what I thought as well, that knowledge definitely isn't forever. Why not comment on the fallacy contained in the meme?