The most important aspect of business planning (the "What does it all come down to?" part), however, is spending the time to do your research ("due diligence") and critically thinking about these various aspects of your business. Of course, it is impossible to anticipate every detail simply by spending time thinking and writing; it is for this reason that plans are referred to and viewed as "dynamic". However, the more issues and scenarios you are able to come up with ahead of time, the more prepared you will be to handle these as they arise.
Finally, a business plan should be error - free. This is important because your business plan defines who you are as a business person. If it turned out sloppy, then that does not speak too highly of you.
Now that you realize its importance, the next thing that you should start working on is learning how to make one. But before you have the urge to get your computer going and start writing, here are the qualities of a good business plan that you have to keep in mind.
If your answer is no, you may have been able to easily accomplish this goal by planning for such expenses in advance through a business plan. Even if having cash at the ready is not a viable alternative for you, you may have planned to have a line of credit available for such opportunities, knowing that in your field these opportunities do arise from time to time.