It doesn't force the letters into the correct slot. It will definitely still let you goof. The "hard" part is that you have to use the letters you guessed. Many people use follow up words to try and guess more letters. For example, you could open with "Pantry" and miss all letters except "r". In normal mode you could follow with "Guise" but in hard mode you cannot because you hit "r" on your first guess.