Every decision you make is actually an exchange. You are exchanging what you could be doing for what you choose to do instead. To the extent you choose and carry out those actions that most effectively lead to what you correctly believe is most important, you will maximize the joy you experience in life.
One way to view productivity is as the practice of acting so as to maximize what you believe to be of greatest value. In order to do this, you need to know what options exist and then prioritize what generates that which you believe to be of greatest value, and your beliefs are what reveal to you what those actions are.
In order to prioritize your actions, you have to understand their cost and their benefit. If you don’t know how much time, energy, and other resources an action will require, you can’t prioritize it against other potential actions. Beliefs are how you will correctly calculate the net benefit of each potential action, which is required in order to prioritize them and select the most effective alternative.
Correct and complete beliefs are essential for correctly perceiving and believing the long-term effects of a potential action. Impact is Pareto distributed: among any set of potential actions, a few will tend to result in outcomes better than the rest combined. Among any set of choices there tends to be at least one option dramatically better than the others. The most valuable choice among a set of possibilities will almost never seem to be the most valuable choice when evaluated in normal ways by a normal person. To the extent you can properly anticipate the importance of each option for potential action and you choose what has the greatest importance, you will accomplish orders of magnitude more than anyone who does not, without any need for any additional resources over what you presently have. If that doesn’t sound like an impossible magic trick, you have not yet grasped the positive effects such an outcome would have.