For words that only have 3 letters, there is no 4th letter. By way of example with the word “increase”, there isn't any a lot more letters afterwards and thus needs to be the word "increase". The word “addict” is from the BIP39 wordlist however , you might have made https://mylittlebookmark.com/story4651811/facts-about-bip39-seed-phrase-word-list-revealed