For words that only have 3 letters, there isn't any 4th letter. For instance with the word “insert”, there are no a lot more letters Later on and therefore has to be the word "insert". The word “addict” is from the BIP39 wordlist however you would've utilised “addi” for “addict”. https://worldsocialindex.com/story4128974/the-2-minute-rule-for-bip39-all-words