system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is a 4-digit code sufficient for banking purposes but not for most online accounts?
gpt
Something you know, something you have, something you are. Those are the three types of security. 

With a card *edit: and the aforementioned ATM pin* you check two of those (have and know), so the individual security of each can be less. 

With an online password you only have one (know), so the requirements need to be a lot stricter to compensate for not checking off the other two types of security.