Even the best models of the world are imperfect. This insight is important to remember if we want to learn how to make decisions and take action on a daily basis.

For example, consider the work of Albert Einstein.

During the ten year period from 1905 to 1915, Einstein developed the general theory of relativity, which is one of the most important ideas in modern physics. Einstein's theory has held up remarkably well over time. For example, general relativity predicted the existence of gravitational waves, which scientists finally confirmed in 2015—a full 100 years after Einstein originally wrote it down.

However, even Einstein's best ideas were imperfect. While general relativity explains how the universe works in many situations, it breaks down in certain extreme cases (like inside black holes).

In 1976, a British statistician named George Box wrote the famous line, “All models are wrong, some are useful.”

His point was that we should focus more on whether something can be applied to everyday life in a useful manner rather than debating endlessly if an answer is correct in all cases. As historian Yuval Noah Harari puts it, “Scientists generally agree that no theory is 100 percent correct. Thus, the real test of knowledge is not truth, but utility. Science gives us power. The more useful that power, the better the science.”

Even Einstein's work was not perfect in all cases, but it has been incredibly useful—not just for increasing our understanding of the world, but also for practical purposes. For example, the Global Positioning Systems (GPS) used in your phone and in your car must take the effects of relativity into account to deliver accurate directions. Without general relativity, our navigation systems wouldn’t be accurate.

What steps can we take to make decisions, given that no single way of looking at the world is accurate in all situations?

One approach is to develop a broad collection of frameworks for thinking about the world. Some experts refer to each framework as a “mental model.” Each mental model is a way of thinking about the world. The more mental models you have, the more tools you have in your thinking toolbox to make decisions.

For example, here are three ways of thinking about productivity:

Are any of these models perfect? Of course not. But if you combine them, then you have a strategy that can help you take action right now (The 2-Minute Rule), a strategy that can help you plan your day more effectively (The Ivy Lee Method), and a strategy that can help you maintain consistency in the long-run (The Seinfeld Strategy).

You need a collection of mental models because no single framework can work in every situation.

Accepting that all models are wrong in certain instances is not a license to ignore the facts. As a society, we should search for better answers, look for evidence, and strive to increase the accuracy of our knowledge.

At the same time, there is a common peril on the other end of the spectrum. Too many people waste time debating if something is perfectly correct, when they should be focusing on if it is practically useful.

We live in a world filled with uncertainty, but we still need to get things done and make decisions. It is our responsibility to develop a way of thinking about the world that generally fits the facts we have, but to not get so gummed up thinking about things that we never actually do anything. As Harvard professor Daniel Gilbert puts it, “The world doesn’t have the luxury of waiting for complete answers before it takes action.”

Impartial answers are the best we have. Focus on what is practical and take action. All models are wrong under some circumstances, but the important thing is if they are generally useful.

One of the hardest things in life is to know when to keep going and when to move on.

On the one hand, perseverance and grit are key to achieving success in any field. Anyone who masters their craft will face moments of doubt and somehow find the inner resolve to keep going. If you want to build a successful business or create a great marriage or learn a new skill then “sticking with it” is perhaps the most critical trait to possess.

On the other hand, telling someone to never give up is terrible advice. Successful people give up all the time. If something is not working, smart people don’t repeat it endlessly. They revise. They adjust. They pivot. They quit. As the saying goes, “Insanity is doing the same thing over and over again and expecting different results.”

Life requires both strategies. Sometimes you need to display unwavering confidence and double down on your efforts. Sometimes you need to abandon the things that aren’t working and try something new. The key question is: how do you know when to give up and when to stick with it?

One way to answer this question is to use a framework I call the 3 Stages of Failure.

This framework helps clarify things by breaking down challenges into three stages of failure:

Centratel provided 24/7 telephone answering service for doctors, veterinarians, and other businesses that needed the phones to be answered at all hours, but couldn't afford to pay a staff member to sit at the desk constantly. When he bought the business, Carpenter hoped that Centratel “would someday be the highest-quality telephone answering service in the United States.”

It was March of 1999. Jeff Bezos, the founder of Amazon, had just announced that his company would launch a new service called Amazon Auctions to help people sell “virtually anything online.” The idea was to create something that could compete with eBay. Bezos knew there were millions of people with goods to sell and he wanted Amazon to be the place where those transactions happened.

Greg Linden, a software engineer for Amazon at the time, recalled the project by saying, “Behind the scenes, this was a herculean effort. People from around the company were pulled off their projects. The entire Auctions site, with all the features of eBay and more, was built from scratch. It was designed, architected, developed, tested, and launched in under three months.”

There is a 4th stage of failure that we haven't talked about: Failures of Opportunity.

These are WHO mistakes. They occur when society fails to provide equal opportunity for all people. Failures of Opportunity are the result of many complex factors: age, race, gender, income, education, and more.

For example, there are thousands of men my age living in the slums of India or the streets of Bangladesh who are more intelligent and more talented than I am, but we live very different lives largely because of the opportunities presented to us.

Failures of Opportunity deserve an article of their own and there are many things we can do as individuals and as a society to reduce them. However, I chose not to focus on them here because Failures of Opportunity are difficult to influence. Meanwhile, your vision, your strategy, and your tactics are all things you can directly control.

For example, Failures of Tactics can occasionally create enough havoc that you mistakenly believe you have a Failure of Vision. Imagine how Sam Carpenter felt when he was working 100 hours per week. It would have been easy to assume that his vision of being an entrepreneur was the failure when, in fact, it was merely poor tactics causing the problem.