The Apple engineer who invented autocorrect for the iPhone and spent over 15 years at Apple is Ken Kencionda. He says there were several fails with autocorrect. Your phone tries to guess what words you meant based on where your fingers land, and what other words are around it. There is also a static dictionary and a dynamic dictionary. The static, is the one with words it knows. The dynamic dictionary is words that YOU use, like a slang word or a common name you give something. It doesn’t always use the dynamic dictionary first. To fix it, go to settings, general, keyboard, and then finally, text replacement. You can put in a shortcut for your favorite word… like duck.