You only need 1 investor - so long as they have enough cash for your needs and fall under the "good/adds value" category. To me, that should equal a hurrah rather than a sigh.
In a past life, I built a company with backing from a single investor. If you're going to go down the path of building a company that requires outside financing, you can never assume that a single investor has "enough cash" to meet your future needs.
Your investor could be a billionaire and there are still countless reasons he or she might not be able or willing to provide additional financing. Just a handful: legal problems, health problems, travel, divorce, death.
