I could probably remember one or two things like that key, but retaining it over the years would be questionable... I used some of my favorite quotes as the passphrases for some of my crypto wallets, and once spent an annoying week when it turned out I misremembered one of them and lost access to some bitcoin. Not a huge value - it's about $1k worth now - but still unpleasant, and I had to spend quite some time figuring out how to recover it (fortunately, it worked). So since then I'm more careful about "I'll surely remember it" thing.

>>My memory is average but when it comes to numbers...

Where I live, memorizing a 25 char alphanumeric is not average. It's not more, either.