In 1905, Albert Einstein showed us that time, energy, mass, and speed are intertwined.

The faster you move, the more energy you need.

The faster you move, the slower time passes for you.

The faster you move, the more your mass increases.

Reaching maximum speed, the speed of light, would require an infinite amount of energy and would mind-bogglingly, for you, bring time to a halt.

His formula, E=mc^2 mathematically describes how these principles apply to our physical world. But the concepts ring true for our daily life too.

Bust your ass too hard, and you’ll fall into bed exhausted.

Bust your ass for too long, and seconds will feel like minutes.

Bust your ass for too hard and too long, and you’ll feel as though you need an infinite amount of energy to go on. The “weight” of your work will become unbearable. You’ll burn out, falling to ground zero (or below).

You don’t think of Einstein’s equation while at work, but you feel the ramifications of overdoing it. You know deep down which tasks suck your energy and which tasks recharge it. And you instinctively know when it’s time to call it a day.

As it turns out, these feelings are key to maintaining the intricate balance between Einsteins four variables—time, speed, mass, and energy—which in turn is the key to becoming maximally productive.