As children we’re all scientists. We constantly come up with theories, and then test them. For example as a toddler you might have had the theory that a glass will easily survive its fall from the kitchen table

A theory, which you probably quickly went on to disprove, much to the frustration of your Mum and Dad.

Nowadays, since we’re grown up, we don’t see theories as what they are any more: educated guesses.

If you come up with the theory that your software startup needs 1,000 clients to thrive and start turning a profit, you almost instantly accept it as true, which leads to lots of disappointment, should you fail in spite of reaching that goal.

Author says a theory is nothing more than a model, which correctly explains a big number of observations.

This has 2 great benefits:

You can make definite predictions about the future.
The theory can always be disproven, if evidence against it comes up.
For example, a commonly accepted theory until 1903 was that nothing heavier than air could fly. That’s what kept 99% of people from driving their carriages over cliffs and jumping out of windows with wings attached to their back.

According to the theory, they wouldn’t be able to fly, and some of the people who tried added credibility to that theory.