You have been told for so long, an open door means opportunity. But once you check the record, it becomes evident that is not always the case. In fact, the value of capitalizing on closed doors can be far more lucrative.
Don't blame yourself if this sounds confusing. After all, this ideology is the antithetical of what we accept to be true; and that is precisely where from it derives value.
Our subconscious mind associates conditions in our environment with prior experience, to act as a reflex. For example, a dry lake means here's no water to be had. -No digging, no second-guessing. The entire process happens so quickly that we often believe we made the decision. In reality it is only when we challenge that reflex, that we become consciously cognizant.
In business, the same true. In fact, your idea could become wildly successful, given the more remote, or unlikely the venture will pay off.
Take the idea of 'greater risk, greater reward' and apply it to something as unlikely as peddling ice to the Inuit. Seems pretty useless, doesn't it? However, if you bet on the likelihood that they'll buy colored ice, the "closed door" concept begins to take shape.
Well that is precisely what Apple achieved during the last 15 or so years. This is also known as a "Blue Ocean Strategy". In that time, the company made products which had a similar function to competitive electronics, but were essentially non-functional when not tied direct to the manufacturer, thus creating their own market entirely.
So no matter the scale of your dream, remember that success is a relative benchmark.
What does matter, is this: Do not let your doubts do the talking. Harness your passion, discover your purpose and use the energy to reach your goal.