All the possible technologies that exist today to keep crypto safe is not worth anything if it is not used in the right way. Most agree that hardware wallets are safe way of keeping crypto, and for now it is shown that this is correct. But security of hardware wallet is worth nothing if user is not aware of importance to make backup of seed words, so in case device is broken or stolen coins are lost.
My opinion is that the biggest challenge is how to educate people to use the available technology in the right and safe way, which is crucial for security of their coins. When something bad happens, then it's too late.
The main problem for me is passwords. I have bad memory, I always lose my passwords. I have lost access to all encrypted stuff because I lost the passwords.
Why you use only your memory for passwords? Nobody is so perfect to remember hundreds of passwords, and the simplest solution is to write them down of paper. Then you only need to store that paper in the best possible way, there is no great wisdom in that.