The probability of a particular state of happiness is equal to the proximity of your energy value to the state of happiness, or in other words, the difference between your state of happiness and the state of happiness being pursued. Therefore, the more alike in nature does your state of happiness become to the state of happiness being pursued, the more probable does that state of happiness become, and once they approach infinite likeness to one another, the targeted state of happiness is then achieved.
Therefore, since all desires are of a specific energy value, their fulfillment is also of a specific energy value, and all that must happen for you to achieve them is that you be as happy as you would be were the desire to be fulfilled. Ergo, the only reason a particular desire could ever go unfulfilled is due to your never being as happy as you would be were it to be fulfilled, but were you to ever achieve such a state of happiness, the desire would then be fulfilled.