The underlying reason a startup is so hard, so strange - and why so many fail - is that you yourself have to figure out what to do.
Throughout life, and most of human history, we have been told what to do. Whether it is learning to farm from our parents, learning to hunt and gather from our parents, learning to memorize and behave in school, getting our first job - there's usually a neat playbook on what to do and how to do it. Sometimes, we even face punishments for not doing what we are supposed to do.
We become experts at doing and not figuring out what to do. We really should be experts at both. Failing at the latter creates countless consequences. Consider Peter Thiel's story in Zero to One, where he recounts incessant competition throughout childhood culminating in being hired at the most renown law firm, only to desire nothing more than to leave it promptly (as the others in the firm did).
Thiel never asked why. He never spent time figuring out what to do. He followed the playbook, followed others, and simply did.
When you force yourself to start a startup with a completely new business model, you have to figure out what it is you are going to do. What customer segment is best to start with? What channel is best to activate those customers after Customer #1000? What partnerships will I need in order to bring this product to market? And this proceeds in this manner for years. It is a new way of thinking for most people.
The most often cited reason that startups fail is because they produced a product that no one needed. Why? Because the founders had an idea and immediately transitioned to doing, never asking, "What is it that I am doing and why?"
Even if you're not intent on creating and validating some entirely new business model, you should ask yourself why it is that you're doing something. And then figure out if that is truly what you want or should be doing. I have no doubt it will help you lead a more fulfilling life.