Success isn't like temperature. There's no measurement tool you can wave around and get an objective reading on exactly how successful you are. Success is self-defined, and there's a lot of anecdotal evidence out there that many of us, including many outwardly successful entrepreneurs, are pretty lousy at judging our success

Humans are naturally wired to focus on the negative. That kept us alive back in the day when a lion could be lurking behind every bush. But today our tendency to overweight problems and take achievements for granted means that many people find themselves in the strange position of being pretty darn successful but still being blind to that success. 

Evaluating your success requires self-examination and reflection. But even that's complicated. You might think that the successful are full of confidence and unbroken good cheer. But that's not what science, experts, and even simple observation reveal. Some forms of mental discomfort actually signal success. If you feel them you should congratulate yourself on your progress not beat yourself up for your self-doubt. 

1. Intellectual humility. 

Remember back when you were a grumpy 14-year-old and you thought you knew everything and adults were all dumb and out of touch? Did you actually know everything then? 

We can all look back and laugh at our youthful arrogance, but it's easy to forget to continue to remember you're probably wrong a lot of the time as an adult too. Intellectual arrogance was silly when you were a teenager, but according to both a ton of science and some of the smartest people in business, it's also silly when you're grown. 

Being willing to doubt your beliefs and hear alternative viewpoints and fresh evidence is a sign of intelligence. This sort of intellectual humility helps you learn faster, spot fake news, connect openly and honestly with others, and become more tolerant of difference. Not being sure what you believe can be uncomfortable but it is also a sign of a mature mind. 

2. Imposter syndrome

Perhaps you've heard of the Dunning-Kruger effect. This much-cited psychological principle says that the most incompetent are often the most confident because they don't know enough to understand just how incompetent they are. It's useful to have a scientific explanation for your office's most annoying blowhard, but many of us fail to consider the flip side of Dunning-Kruger: If ignorance can breed unearned confidence, then advancing knowledge can lead to doubt. 

If you worry about your skill level, that's actually a good indication you understand your field well enough to see its full complexity but haven't yet settled into intellectual complacency. And your self-doubt is likely to spur you toward greater excellence. Perhaps that's why research shows those who report suffering from imposter syndrome actually perform better at work

3. Questioning the value of "success" itself. 

The grass always looks lush when you're peeking over the fence. But actually manage to get yourself into the hallowed circle of "success" and often you'll discover you're actually standing on Astroturf watered with tears.

This isn't just because lots of outwardly successful people are pretty miserable (their cheery online personas notwithstanding). It's also because many people pursue worldly "success" -- big bank accounts, fancy job titles, the esteem of their peers -- without thinking deeply about whether that's what life is really about. The result is that a lot of us spend our early years battling to attain something that, once we have it, just makes us realize we were chasing the wrong goals all along. 

If you've reached that stage, it's a good sign. It shows you now have the stability and self-awareness to start pondering your true values and setting your own course. 

As Brianna Wiest has observed on Thought Catalog, "when you start to become truly successful, you also start to realize how little it matters. You will start to realize that it is not the answer to your problems, and that you also value the people in your life, your down time, and your ability to enjoy your days. True success is realizing that success is not everything people think it is, and it is a privilege to be able to know that."

So, are you successful? Only you can answer that question. But don't be led astray by thinking that successful is synonymous with a lack of self-doubt. It's not. A troubled mind can often be a sign of the sort of questioning and questing that means you're doing pretty well in life already.