Drishti is usually translated as gaze, which makes it sound mystical. It is not. It is simply where you point your eyes in a pose, and it does something concrete: it steadies the head, and the head steadies the balance.
What changes.
Try it. Stand in tree pose and let the eyes wander around the room. Now fix them on a single still point at eye height and leave them there. The pose stops wobbling almost at once. The eyes were feeding the body a moving picture; a fixed gaze feeds it a still one, and the body holds still to match.
There is an attentional half to it as well. A settled gaze gives the mind one less thing to chase. The eyes stop shopping the room; the attention stops following them. This is why each traditional pose has a suggested drishti — not as doctrine, but because it works.
You do not need to memorise them. The rule underneath is enough: in any balance, find one still point and leave your eyes there. The pose will thank you.