Can you guess the meaning of the idiom 'sleep on it' from looking at the picture?
To sleep on something (sleep on it): to wait until the next day (in order to think carefully) before making an important decision.
What's "IT" in the picture above? "It" is any decision that you have to make.
It's a way of saying that you need more time to think about something and you don't want to make a quick decision that you may regret or feel sorry for making later.
Also, being able to sleep not only gives you more time but it gives you a chance to NOT think about the issue for awhile. Sometimes, when you think about things so much you actually feel more confused and stressed out.
So, if you can sleep, you are able to relax your mind and get rest. When you wake up the next day you can think about the issue again and make a better decision than if you were rushed.
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This will help you practice your English and remember this idiom in the future. No pain no gain (it's hard to practice but if you don't do it your English will not improve). Do you like to sleep on things before making decisions? Is it difficult for you to ask for permission to sleep on something? When is the last time you decided to sleep on anything?