It helps but is not a requirement, depends on what you are trying to accomplish.

All of Dave's early winners were between a 10 to 20 x return on investment, about a 3x return on his overall portfolio, with an investment return period of around seven or eight years.

With 500 Startups, they aimed to find a "unicorn" only 1-2% of the time, but given that low probability of that even, their portfolio size needed to be a minimum of 50 to 100 companies to even have a shot at that.

So when thinking about investment, you need to know what return multiple you are trying to hit, how likely your companies are to return, and then you would know whether or not you need a unicorn to do it, or how many unicorns at that.