For words that have only three letters, there is no 4th letter. Such as with the word “insert”, there won't be any more letters Later on and thus need to be the word "include". The word “addict” is during the BIP39 wordlist however, you would've utilized “addi” for “addict”. The https://socialeweb.com/story4193022/bip39-phrase-generator-can-be-fun-for-anyone