Like Amur said, the pillars of Mercy and Severity are a core idea in magical qabala, Golden Dawn etc. The famous Middle Pillar rite is the pillar in between them, sometimes called the Pillar of Mildness or the Pillar of Consciousness.
You might have seen them on the high priestess tarot card - she sits between a black pillar and a white pillar.
A different way to think of them can be "force and form" or "energy and structure". So the Pillar of Severity isn't just laws and punishment, it's also the riverbank, the vessel that contains, the magic circle, the laws of physics, DNA, iambic pentameter, etc etc. Force and form are the dyad necessary for creation (the concept of force and form comes from Aristotle, but the early qabalists and hermeticists were aware of it).
But of course in classic as-above-so-below-style, it also applies to life. Life is always a phased balance between expansion and restriction
But I'm not sure what you mean by this, or maybe I understand but disagree. It seems to me the aim of a lot of personal development is to see past false binaries to the full spectrum of possibilities. There are always more than two choices.
(I just spent some time trying to think if I could come up with a situation where there were genuinely only two choices, and I couldn't think of one.)