Some things start under our control, but once they get going, they take over completely. They drag us along with their own momentum and give us no way back. Think of someone who jumps off a cliff. Once they're falling, they can't control where they go. They can't slow down or change direction. Their reckless decision has left no room for second thoughts or regret. They have to go wherever gravity takes them, even if they could have avoided it. The mind works the same way. Once it gives in to anger, love, or any other strong emotion, it can't stop itself. Its own weight and the pull of vice will carry a person down and throw them into the deepest trouble.
There are certain things whose beginnings lie in our own power, but which, when developed, drag us along by their own force and leave us no retreat. Those who have flung themselves over a precipice have no control over their movements, nor can they stop or slacken their pace when once started, for their own headlong and irremediable rashness has left no room for either reflexion or remorse, and they cannot help going to lengths which they might have avoided. So, also, the mind, when it has abandoned itself to anger, love, or any other passion, is unable to check itself: its own weight and the downward tendency of vices must needs carry the man off and hurl him into the lowest depth.