system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What's the point in having a strong password if most passwords are stolen from the server end rather than from brute force hacking a single account?

Your password must be at least 8 characters, with a number, uppercase letter, and special character. Then their server gets hacked and 30 million passwords are stolen. So why bother?
Are the passwords encrypted within their server and a complex password makes it harder to retrieve from the stolen passwords? Either way I don't get it..
gpt
If the passwords are properly stored, they'll be hashed. This means that your password itself isn't stored, but only the result of a calculation that's based on your password. Strong algorithms aren't reversible, so when someone has the database the only way for them to find out what the password is, is to guess a password, calculate its hash, and see if the hash matches. (The website should also use a "salt", a random value unique for each user, to calculate the hash--this means that two users with the same password will have different hashes, and hashes from some other cracking attempt can't be used.)

Strong passwords are harder to guess in this way. Even if you can guess thousands of passwords per second, it will take an extremely long time on average to guess something like a 15-character random string. This provides time for the breach to be uncovered and then for you to change the password.

Note here that you should still assume your password is compromised. A cracker could get lucky, or the website could have used bad algorithms for the hashes that are easy to crack. This is why it's very important not to reuse passwords between websites. On the other hand, no matter how many precautions the website takes with password storage, they will all fail if your password is easy to guess.