BG Chap 18 - Happiness in the mode of goodness
That happiness which brings joy and destroys sorrow with practice, which appears to be poison in the beginning but becomes nectar, and which awakens one to self realization is in the mode of goodness. It arises because of satisfaction coming from repeated practice – not a sudden appearance of satisfaction as in contact with sense objects. In the beginning it appears to be poison, filled with lots of suffering because it is difficult to control the mind, since one has not realized the soul as distinct from the body. But it later becomes sweet, like the falling of streams of nectar, with the attainment of samadhi, from realizing the soul. This happiness arises from intelligence which has been purified by concentrating on the atma.