1. The Blank Page.
You start out with a general idea of where you're going, but there are no constraints - you can go anywhere. The choices can be overwhelming. You spend a lot of time meandering and no small portion completely lost. Your final destination is practically invisible until you're practically on top of it.
2. The Work.
It is so much more work than it looks like. Every day you realize it requires another skill, another domain of knowledge, another chunk of time that you have to find a way to acquire.
3. The Qualification Paradox.
You know perfectly well you are woefully underqualified, and also that the only way to become qualified is to just do it. So you fake it 'til you make it: spend every day pretending to yourself that you can do it until you discover you've actually done it.
4. The Business.
You have to figure out who you're selling to, what they want, how you can give them something they didn't even know they needed that can only come from you. You have to figure out who you want on your team and how to attract them and how to deal with them. You have to figure out where the time is going to come from.
5. The Investors.
You have to decide if you want outside investment, who would be the best fit, and then polish your pitch. And polish it some more. And realize in the process that your product needs work and go back and polish that, and then come back and polish your pitch all over again. Repeat.
BONUS. The Courage and the Faith.
There is every reason to believe you will fail, and that it will hurt. This is why most people will never try. But those who do, who take the leap of faith, will tell you that creating something is a journey, not a test. The concepts of success and failure over time are far murkier than you'd imagined. At the end of the day, it is your journey and your courage that will make you proud and bring you happiness.