The workings of the financial markets seem like quantum physics. The impossible happens all the time. It is just a matter of scale. In physics things get weird when we look at very small things. In finance things get weird when the numbers get big.
Two photographs from the City- source of much weirdness.
Have only one credit card (cash back preferred) and pay the bill in full every month. If you seem too desperate for credit this may work against you.
Excessive unused credit means you have the potential to get in trouble later on. A single line of credit is good. Twelve is bad. None is even worse.