Why exactly do we need a backup?!

Why exactly do we need a backup?!

In your subconscious, you expected that may your local hard drive will be corrupted. Or your important files get deleted accidently. Or -as common in nowadays- a ransomware can corrupt/delet/lock your files. Or even for the future use, when you will upgrade your laptop. Your data will be saved and ready to be located to another home.