Well, every project we do in life starts with the expectation of how would it be if it works. But maybe you should consider the other side: what if doesn’t work?
What if people do not buy your product? What if stocks fall? What if your boss does not approve your idea? What if the supplier does not meet the deadline? What if?
Doing this kind of question makes you anticipate the failure, pushes you to develop a second plan in case of unforeseen events.
Read the story of successful people and you will see that 100% of them failed (and in some cases failed several times) before succeed.
So, consider this: you will fail. But if this is included in your plan, you will be in advantage.