Bhagavad Gita · Sankhya YogaChapter 2, Shloka 41 (2.41)

One understanding vs endless understandings. Vyavasāyātmikā buddhi — a resolute understanding focused in one direction. Its opposite — bahu-śākhā — an understanding spread out and scattered like a tree with countless branches. Shankaracharya: one resolute understanding born of right means of knowledge cuts off the branches of the contrary understandings; it is through the endless varieties of contrary understandings that samsara becomes endless and vast, and when those varieties are stilled by discerning understanding, samsara too is stilled.

Ramanuja's particular meaning: In the action of one who seeks moksha, the understanding is vyavasāyātmikā, because it rests on a firm grasp of the true nature of the self. In kamya karma (actions done for their fruits), the understanding is irresolute — because there it is enough to know only that "there is a self distinct from the body", without a firm grasp of the self's nature; and because of the desire for fruits such as heaven, that understanding is divided into many branches.

Its meaning today. When our mind is scattered among a hundred desires at once — I want this, and that, fear of this, worry about that — we get nowhere. A clear, firm direction gives the understanding strength.