It’s not easy to spot your own mistakes when you write. Even the professionals get it wrong sometimes.
Can you spot the error on the front page of The Observer?
I had such faith in the paper that I looked inside to see if something new called a skycraper had been invented.
It hadn’t. You guessed it, they were talking about skyscrapers.
So check and check again. And if possible get someone else to read your work. It’s much easier to pick up someone else’s mistakes.