For words that only have three letters, there's no 4th letter. For example with the word “insert”, there isn't any a lot more letters Later on and thus need to be the word "include". The word “addict” is in the BIP39 wordlist however you would've used “addi” for “addict”. To https://dmozbookmark.com/story18837146/the-definitive-guide-to-bip39-seed-phrase