Confused by concept of a Weak Acid

[Brandon Achugbue 3H]

So I understand that weak acids are incompletely ionized in water, where there's some equilibrium to describe the concentration left between the original molecule and the dissociated ions, but I don't quite get why this is happening. Why is it not one or the other?

Let's use the Carboxyl group COOH for example.

If a compound is more stable in the form of its dissociated ions in water (COO- surrounded by water and H+ surrounded by water), then why would some of it decide to stay in the original molecular form, or decide to go back to its original molecular form? I can see how an Acid that becomes a Conjugate Base might find a more stable setup by bonding with some new molecule, but if it's just between the original molecule and the dissociated form, why would it be indecisive as to which one is more stable? And if it is more stable in molecular form, why would any amount of it be ionized in the first place?

My best guess is that there are competing factors in deciding which form the molecule / ions choose to stay in that are hard to quantify (and out of the scope of this class) - like maybe the strength of the acid corresponding with its original bond lengths is being compared with the strength of the acid corresponding from the resulting anion's stability (if there's resonance or electron withdrawing atoms), and there's some order to these interactions occurring that we don't know about.

In this case, the H+ given off by COOH would have the same O-H bond in either case (the molecular form COOH or dissociated form COO- H+), but COOH is stabilized by resonance. If it is so stable in its molecular form, what about the interaction with water makes it able to break off an H+ in only some of the molecules?

[Emma Swanton 1G]

I think it's because the compounds are constantly dissociating and reprotonating no matter how stable they are, but the stability of the acid and the conjugate base determine the rates of the forward and reverse reaction. The molecules are constantly interacting with each other and causing reactions when they get close enough to each other. Even conjugate bases of strong acids reprotonate sometimes, but the pKa is so low that it will immediately dissociate again. I hope this helps!