• What if the idea is already taken?
• What if people think it's a dumb idea?
• What if my marketing strategy doesn't entice people?
The list of doubts can be extended pages down if given ample time. Excessive thinking inevitably leads you down a road that stops with a dead-end sign. You may feel that it's pragmatic to think things through and have all bases covered, and to a degree that's correct. However you can ponder and research for years, even decades, and you still won't have mitigation for every possibility. This is what I call thinking yourself into a hole. Thinking has to stop at the inflection point where analysis turns to doubt and paranoia. You don't need many reasons not to do something; just one compelling reason is enough to stop you. The thing is there's always a compelling reason not to action any idea.
An idea locked in the chamber of your mind and suffocated from physical expression will ferment and rot into a wishful fantasy that gets written off. The best part is you will be convinced it wasn't a feasible idea to start off with.