For words that only have three letters, there is no 4th letter. For example with the word “increase”, there aren't any much more letters Later on and thus needs to be the word "insert". The word “addict” is within the BIP39 wordlist however, you would've utilized “addi” for “addict”. Using https://bookmarklinking.com/story4975223/top-latest-five-bip39-seed-phrase-mnemonics-generator-urban-news