Gaining phronesis requires experience.

"Although the young may be experts in geometry and mathematics and similar branches of knowledge [sophoi], we do not consider that a young man can have Prudence [phronimos]. The reason is that Prudence [phronesis] includes a knowledge of particular facts, and this is derived from experience, which a young man does not possess; for experience is the fruit of years."

"Phronesis is concerned with particulars, because it is concerned with how to act in particular situations. One can learn the principles of action, but applying them in the real world, in situations one could not have foreseen, requires experience of the world. For example, if one knows that one should be honest, one might act in certain situations in ways that cause pain and offense; knowing how to apply honesty in balance with other considerations and in specific contexts requires experience."