Investor who hodl 2000 BTC really has to worry about safety of his keys from his BTC digital wallet. The safest variant is definitely to learn those keys. However it’s not a problem for him to withdraw some part of BTC or to pay in BTC for holding his keys somewhere in secret safety bank deposit box. There is one more variant (cheap and risky): to find some secret place in house/flat and to hide there a tiny piece of paper. But I think that I would rather hided keys on my body (made a lot of symbolic tattoos on different parts of my body or one big with hidden small in it) and remember the sequence.