For words that have only three letters, there's no 4th letter. For instance with the word “increase”, there won't be any a lot more letters Later on and thus needs to be the word "add". The word “addict” is during the BIP39 wordlist but you would've utilised “addi” for “addict”. https://ticketsbookmarks.com/story18724607/bip39-seed-phrase-mnemonics-generator-an-overview