It's very risky, I just have to remember it and not write it down on paper because I know I might forget it someday because I don't use it every day. In the early days you can remember it so easily but you don't know if you will still remember it easily a few months later. Forgetting even 1 word you will not be able to access your wallet and it is a nightmare. So, writing it down on paper and keeping it in a safe place is the best choice.