In the rainy season, both pearl and hailstones are produced. Being of the same form, a pearl is considered good doer while the hailstone causes damage.
Hailstones destroy/damage crops and other vegetation, whereas a pearl is praised for its beauty and lustrous form.
Being damaging in nature, a hailstone melts away in no time, whereas a good doer pearl remains stable.
Similar is the effect of the company of vice/evil and virtuous people. The supreme wisdom acquired by the teachings of a True Guru and polluted intellect due to base wisdom cannot be hidden. (163)