To a startup, having a strong and clearly articulated vision is important. 

A startup is essentially operating from a clean slate, with no existing products or sales commitments encumbering them. It can work on anything at all in the world and aim to be successful around it. 

But it very quickly needs to lay a marker on that clean slate in the form of a vision. 

A vision helps it decide what problems to solve, and what to ignore. It helps decide on what customers to target and whom to ignore. It helps decide how much effort to expend in a certain direction before re-evaluating it's position and direction. It helps decide what kind of employees to hire, what kind of investors to bring on. 

In essence, a strong and clearly articulated vision puts constraints on the startup to focus only on what's important as well as help define what is important and what isn't. 

Like putting the proverbial blinds on a horse that keeps it from being distracted from what's on either side and focuses it only on the road ahead.

An individual without a vision is like a startup without a vision. 

They have no constraints on what direction to dedicate their time, their efforts at learning new things and picking up new habits. 

However, having a vision brings clarity and helps them decide what opportunities to say yes to and what to say no to.