I like reading science fiction books

I like reading science fiction books

These two strings are printed the same way, but the first uses single quotes, and the second uses double quotes.

I think $book is my favorite book

I think catch-22 is my favorite book

These two strings are still printed the same way, however the first uses single quotes and interprets the variable literally and prints it.

In order to ensure strings with elements like variables are printed as intended, be mindful of the difference between single and double quotes.