I recently had a conversation about nutrition that turned into a bit of a debate. I’m sure you’ve heard it before: “I eat this, you should try it!” “No, you should eat this! And that other thing, right after you exercise.” “OK, but do it in small portions, regularly throughout the day.” “No no, it’s all just calories in, calories out.”

We could have argued for hours, if we hadn’t realized something that stopped us in our tracks: we all had different goals in mind. “Wait, wait. You’re talking about losing weight, right? And you must be talking about physical fitness. And I’m just talking about being healthy.” Smiles all around, bitter argument averted, we moved on to more important matters: deconstructing the latest Internet meme.

We tend to think other people are like ourselves. Sure, we can spot outward differences like height or age, but deeper personality traits are more difficult. We know which of our friends are athletic, or thoughtful, or funny, but maybe not that Alice tends to overspend on hotel rooms, or that Bob avoids clothes with visible logos.

Even if we do know those things, it takes too much mental energy to pull them all into working memory every time we talk with someone. Instead, we take a shortcut: we substitute ourselves. We know our own beliefs and preferences intimately, so it’s trivial to imagine what we would do in any situation.

This usually works well. Human nature is a powerful force, and it’s made us much more similar than we are different. This substitution technique is so successful that we all adopt it early in life, and it becomes so automatic that we rarely notice when it happens. Daniel Kahneman describes this in elegant detail.

Unfortunately, we’re not all identical, so substitution sometimes guesses wrong. That wouldn’t be so bad if we were aware of it, but it’s so ingrained that we blame the other person, or the communication medium, or anything except our own lazy, shortcut-prone brain.

We often see this in practice when we assume other people share our goals. Whether it’s a political debate, brainstorming at work, or a family meeting, people often skip straight to problem solving mode. They don’t bother to check that they have the same goal in mind, or even if they agree on what the problem is!

Keith Ferrazzi’s book Never Eat Alone is one of my favorite examples. It’s about networking and building business relationships, and not surprisingly, it advocates always having lunch with other people.

I understand the idea. I also treasure the occasional chance I have to eat alone. I’m an introvert, so being with people drains me, and some work days are so packed with meetings and collaboration that I need that alone time to recharge my batteries and get through the day.

At first, I thought the book was silly and misguided. I couldn’t help but wonder if it might be on to something, though, and maybe the problem was on my end. I eventually realized that we just had different goals.

Ferrazzi assumes that everyone wants to succeed in business, so his recommendation is normative for everyone: never eat alone. Business and career are all well and good, but they’re not high priorities for me. If recharging at lunch means I end up with fewer business relationships, so be it. Ferazzi and I are both right; we just have different goals.

What’s the takeaway? Pay attention to your assumptions. Try to notice when you make a judgment based on what you’d do, instead of what someone else would do. Put yourself in their shoes instead, or even better, ask them explicitly what their goal is. If yours is different, nail down a shared goal first.

Oh, and nutrition? It’s a tar pit. It’s incredibly hard to research scientifically, and the constant fads and pseudoscience outweigh what little decent research there is. Don’t overthink it! Eat healthy foods, moderate, exercise, and do what works for you.