Building a Start-up team:

Many things go into putting a team together to start a new venture. Most often the case is typically, two or more people who have worked together or even studied together or have been friends and shared similar thoughts on some issues, come together and start a company. This is the best case.

We are talking about not so "best case".
You have decided to throw your job and want to be an entrepreneur.

You have a an Idea and you have done enough ground to work to say, that it can be a great success if you take it to market.
Or
You have come across a problem area in your work and think you have the answer for that.

You have a great idea and your employer says that would be deviating our focus and you want to pursue the same.
Or
whatever may be the reason for you to think of getting started as an entrepreneur, you need a competent team.