For words that have only three letters, there's no 4th letter. Such as with the word “insert”, there won't be any more letters Later on and therefore have to be the word "include". The word “addict” is within the BIP39 wordlist however, you would've utilised “addi” for “addict”. Using BIP44 https://bookmarkshq.com/story20576496/bip39-phrase-generator-can-be-fun-for-anyone