Read here cause is HUGE
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This is testament to why you should leave file extension viewing on.
If you are familiar with file types and their icons, then there is no need to display the extensions.
The icon for each file type is usually different so you know what they are. If you are unsure you can right click on the file to go into its properties to find out.
Its important for anyone unfamiliar with icons (and their associated extensions) to educate themselves about them, so they know what type of file can harm their pc.