For those who could have sworn they typed everything correctly, yet keep coming up with the "you're wrong" page:
Some of these quotes have British spellings (colour, humour). One quote has the word "busyness" in it.
Other times, two words with similar spellings can work in context (could/would; size/side).
Not all two-letter words are real words. "TV", "Mr", and such are in here.
The best way to figure out these is to reset the puzzle, type slowly, and watch the remaining letters line at the bottom. At some point, you're bound to discover the letter you duplicated and fix the problem. Or, if you can decide which is the problem word, just keep trying all the remaining letters until you get it right.
Slotted spoons don't hold much soup. - Stephen Sondheim