Why does connecting Positive directly to Ground cause problems?
A short circuit = a wire or any other too low resistance load between the poles of a voltage source or two nodes of a powered circuit.

"Too low resistance" = causes the voltage to drop unusable for its original purposes due the internal resistance of the source 

OR

Causes so high current that some part in the circuit gets hot and is destroyed (the rechargeable batteries are extremely dangerous in this sense)

OR both of them. 

The current regulation prevents the "getting too hot" case. Fuses are the other way to protect.

Innumerable amount of fires, deaths and equipment destructions are caused by short circuits - some of them accidentally, some by using bad parts, some by an intentional action that was not understood and some  intentionally to cause harm. 

Maybe you should as soon as possible learn the basics about voltage, current and Ohms law. Until that avoid messing around electric circuits without competent quidance. 

Your writing shows that you and the people nearby really should be afraid of your actions with electricity.