It's just the way you're built. These are well known limitations of the brain.

This is the reason, for example, why phone numbers are broken down thus:

736-31-21, because your short term memory can only hold three to four figures at a time, thus instead of
seven-three-six-three-one-two-one

you think of it as
seventhirtysix thirtyone twentyone

we're so easy to fool.