If you have ever asked yourself how many hours you have to accomplish a task each day, you are not alone.

The answer has always been the same for most people: 60 to 70 hours in a typical week. According to a study published in journal the Proceedings of the National Academy of Sciences, however, this type of per-hour work has been called into question. The researchers explained that because the reasons for working inefficiently are numerous, there’s no specific task that our brains are programmed to do more efficiently.

With this knowledge in mind, author Brian Cox recently explained that just as time is the only finite resource, so too is human motivation.

“The answer is that people are wired to work for different reasons,” he said on the Superhuman podcast. “There’s a mathematical method of predicting how motivated you’ll be for different work. If you’re working on a math problem, that will tell you right away if your level of motivation is likely to be high or low for that particular task. And so there’s a formula for doing calculations, and your brain has to align its neurons so that it’s focused on that task when the person is supposed to be working on it.”

He continued, “If you’re working on something like super intelligence and people ask you what motivates you to do this, then why do you hate working on it? The answer is human motivation. We’re wired to work for different reasons. And so if you have to balance your work-life balance, then that leaves you with the principal that you can switch your motivation levels to accommodate your work-life balance.”

The problem with this thinking is that the majority of us don’t adjust to our circumstances based on our motivation levels. For most people, there are two motivations they strive for–providing for the people who depend on us, and furthering our own interests and goals. In this sense, performance and interest are almost in direct opposition.

In a world where most of us are incapable of giving 40 hours of our lives to personal goals and pursuits, we must constantly strive to balance both.