than you have brain cells for....

[keannu]

I can't understand "than you have brain cells for" It seems to say "the things you have to remember are more than the number of brain cells", but what is "for" at the end?

ex)Today, everyone has paswords for everything.- from email to bank accounts to online subscriptions to payment accounts. Some people use the same or a limited number of passwords for everything, and if they change them, they apply these changes to everything...But this approach doesn't always work, since some companies have different formats for passwords. As a result, you have to remember more things than you have brain cells for....

[Tdol]

Without for, it just refers to the number of brain cells- which would be a ridiculously large number and far greater than the number of passwords. If you put for in, it suggests that your memory is overloaded and you can't remember all these passwords. You don't have to remember billions of passwords, but enough to be a problem. For makes it figurative- remove it and it's literal.