Here's why:

* Weak acids are acids that only partially ionize (dissociate) in solution. This means they don't completely break apart into their ions (H+ and the conjugate base).

* Strong acids, on the other hand, dissociate completely in solution.

Example:

* Acetic acid (CH3COOH) is a weak acid. When it dissolves in water, it only partially ionizes, forming a small amount of H+ ions and acetate ions (CH3COO-).

* Hydrochloric acid (HCl) is a strong acid. It completely ionizes in solution, forming a high concentration of H+ ions and chloride ions (Cl-).

Key Takeaway:

The degree of dissociation of an acid determines its strength. Weak acids only partially dissociate, while strong acids dissociate completely.