These following mistakes are jarring to readers but go undetected by writers (and many editors). Some of these errors can be attributed to our colloquial speech, but others sneak into ebooks because the word being used improperly is not spelled incorrectly and thus goes undetected by spellcheckers.
Incorrect: "For all intensive purposes". This doesn't make sense. Is each purpose very intense? ...What would that even mean?
Correct: "For all intents and purposes". This means for every practical reason. People accidentally mishear "intensive" instead of "intents and".
Incorrect: "You can get a travel momento at the souvenir shop". Momento is not a word in English, though in other languages it means "moment".
Correct: "You can get a travel memento at the souvenir shop". This memento means "something that serves to remind".
Incorrect: "I was suppose to walk the dog".
Correct: "I was supposed to walk the dog". You cannot omit the "d". The "d" sound is often blended into the "t" sound (supposed to) when spoken so many people mistakenly write this word without the "d". This is the same concept that plagues "Use to" (incorrect! ) and "Used to" (100% correct).