There are 2 concepts to think about, controllability (how easy is it for pilot to change the aircrafts pitch) and stability (how the aircraft resists/reacts to changes in pitch).
An aircraft that is more stable (ie one that tends to maintain its pitch attitude) is less controllable (ie it is less responsive to pilot inputs) and vice-a-versa.
The tail surfaces of the aircraft provide a balancing force to make the aircraft more stable in pitch - if the nose pitches down, the tailsurfaces, rise up and the airflow over them will act to produce a downward force on the tail, this will tend to raise the nose.
If the nose pitches up, the tail goes down and the airflow now produces an upward force on the tailplane, acting to lower the nose.
The aircraft pitches around the CofG position.
Like lifting a long armed lever, if the CofG is more forward, it doesn't need much force on the tail to get it to pitch (making it more stable) however it requires a large up/down movement of the tail to make it pitch by a certain angle (making it less controllable).
With that forward CofG, if the aircraft's pitch is changed, eg by turbulence, the tail will only need to change its angle of attack by a small amount to get it to give enough force to correct for the pitch deviation - so it is more stable. However if the pilot wants to pull up into a loop, they may not have enough control deflection to get it to pitch up as desired.
Conversely a rearward CofG gives you the opposite effect - more controllability - it is easy to pitch the nose up into a loop but you also get less stability - the tail will need to generate more force to correct for unwanted pitch.
Not exactly an aerodynamicists explanation but that is how I would explain it.