system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do credit scores work?

Hi everyone! I am woefully deficient in knowledge about credit scores. While I have good credit, it all seems highly illogical to me especially as I prefer to use my debit card over my credit card. 

Could someone please explain what a credit score is? Why is it important? How it is calculated? And why certain aspects (such as length of time using and amount of use for credit cards) matter? Thank you!
gpt
There's 4 main companies which compile credit data provided by peoples creditors and also companies which harvest public record information like LexisNexis. This data is compiled into a credit file and then provided a mathematical score based on things like credit payment history, revolving usage, and length of credit history. The most important mathematical score is called a FICO and provided by Fair Isaac and not by the credit data repositories themselves.

The formula Fair Isaac uses is not public knowledge but the number is far from arbitrary and ranges from 350 to 850. The credit repositories have also made their own "credit scores" but no lenders use them and their general purpose seems to be to confuse consumers.