The great source of both the misery and disorders of human life seems to arise from overrating the difference between one permanent situation and another -- Some of these situations may, no doubt, deserve to be preferred to others, but none of them can deserve to be pursued with that passionate ardor which drives us to violate the rules either of prudence or of justice, or to corrupt the future tranquility of our minds, either by shame from the remembrance of our own folly, or by remorse for the horror of our own injustice."
it wants to say that We should have preferences that lead us into one future over another. But when those preferences drive us too hard and too fast because we have overrated the difference between these futures, we are at risk. When our ambition is bounded, it leads us to work joyfully. When our ambition is unbounded, it leads us to lie, to cheat, to steal, to hurt others, to sacrifice things of real value. When our fears are bounded, we're prudent, we're cautious, we're thoughtful. When our fears are unbounded and overblown, we're reckless, and we're cowardly.