The problem: Our biggest goals are hardest to achieve because we burn out early. We burn out because we work hard and slack off at exactly the wrong times.

The solution: Do the opposite of what feels normal. Work hard when it’s easy and scale back when it’s hard.

I run marathons, but I’m hardly a leading expert on running. I’ve never followed a formal training schedule, hired a coach, or joined a running club. And I’m not fast—my PR is just under four hours—but I’ve always finished.

Training matters, but what gets me through a race as difficult as a marathon is an approach I take in my life that just happens to help my running, too.

I call it the Law of Equal Effort, and it’s pretty simple: Regardless what life throws at you, put in the same effort.

Following this theory, the progress you make over time can vary significantly but, in the end, you get to the same place and you feel a lot better when you’re done.

Most importantly, you actually make it to the end.

The Law of Equal Effort will help you when you’re taking on a big challenge and you don’t feel confident. You don’t always get to decide when things will be easy or hard, but you get to decide how to deal with the ups and downs when they come.

Here’s how you can put the Law of Equal Effort to work in your day-to-day life, as well as a few situations when you should take a different approach. We’ll apply it to three examples: running a marathon (naturally), building a business, and maintaining a relationship.