Think of your house with a special lock that only opens with a unique key. Now, imagine someone sneaks in through a window you forgot to lock or finds a spare key hidden under a flower pot. This is similar to an authentication bypass. The lock (or login system) is supposed to keep strangers out, but sometimes there are other, less secure ways to get in.
Hackers look for these 'windows' on websites, like using easy-to-guess passwords or finding weak spots in the code that checks if you have the right 'key' to enter. It's like if every house on your street had the same spare key hidden in the same place. A bad guy could easily get inside without you knowing. This is important because it means someone could access your email or bank account without permission.
When websites don't secure all entry points, these sneaky methods can be used by people who want to steal your information or cause harm. So, it's really important for website creators to make sure all the windows are locked tight, not just the front door.