"The rule is, not to besiege walled cities if it can possibly be avoided. "
Sun Tzu, The Art of War
I admit it. I hate to give up, I hate to quit. Especially when it comes to selling and opportunities. So much so, that I constantly have to focus on the shortest path to "No" when it comes to prospecting and selling, and have always been aware of the tendency for people to go down rabbit holes in my sales teams. I always have a saying: "Next". There are too many opportunities and prospects out there to waste valuable time and energy working on opportunities that are hopeful long shots at best. Even back in Sun Tzu's day, they knew breaching cities with built walls was an exercise in futility.
In sales your wall is BANT: Budget, Authority, Need and Timeline. With each check in the BANT box, you break down the wall. You also quickly identify supposed buyers that are time wasters and not serious. If you cannot articulate who signs, where the money is coming from, the person who will sign and the compelling business need, you need to yell "Next" sideline the opp and nurture it, but spend your time on deals that can be moved forward and closed.
You can read more on BANT here and defining the sequence of events: What is BANT in Sales? . And remember, learn how to identify rabbit holes and say "Next" to avoid trying to climb the wall to closing your next opp.