In a game of tennis, the player returning a serve adopts a stance for uncertainty. The player floats from side to side, grazing all options but committing to none. The ball can come from any direction, at any speed and at any time. 

When you're starting out as an entrepreneur, you must be ready for that ball of disappointment to strike you from any direction, at any speed, and at any time.

Like the tennis player returning the serve, your brain must float without being anchored into one single contingency plan, to survive.

Facing uncertainty feels scarier than facing physical pain.

In 2016, a group of London researchers explored how people react to being told they will either "definitely" or "probably" receive a painful electric shock. 

They discovered an intriguing paradox. Volunteers who knew they would definitely receive a painful electric shock felt calmer and were measurably less agitated than those who were told they only had a 50 percent chance of getting the electric shock.  

Your brain's uncertainty "tracker".

Your brain is constantly creating and updating a set of rules that can predict how your world works. A mismatch between its prediction and what actually happens creates a moment of uncertainty.

Your brain's best way out of this uncertainty is either by updating the rules with new information or creating a brand new set of rules with fresh ideas.

For either of these to happen, your brain must break free from old ways of thinking and become fluid and agile enough to adapt, learn and understand.

When faced with uncertainty, it must adopt the stance of the tennis player returning the serve and be ready to respond to any situation. 

A thumbnail-sized structure in your brain tracks uncertainty. It is called the Locus Coeruleus or LC. 

Why uncertainty makes you feel "on edge".

Your LC responds to uncertainty by bringing your brain into a fluid state that can transition easily across different configurations.

Since your brain doesn't know which configuration the uncertain environment will demand, this fluidity optimizes its chances of success in the uncertain terrain.

The LC brings your brain into a fluid state by releasing the neurotransmitter norepinephrine across key regions in the brain.

This release of norepinephrine makes you feel "wired" or "on edge". 

Why is uncertainty scarier than pain?

If you're expecting something to happen (even if it is painful), your brain doesn't anticipate transitioning across different configurations. It adopts a specific configuration that is tailored to the given situation.

Since your LC doesn't need to orchestrate networks across your brain into a fluid state, it does not release norepinephrine in quite the same pattern as it would in uncertainty.

This may be why you feel calmer anticipating pain than you do anticipating uncertainty.

What this means for you.

The jitters you feel during uncertainty are a good thing. They are the result of your brain reconfiguring itself into an optimal state to maximize its chances of success in the face of any challenge.

If you find it difficult to tolerate uncertainty you may be biased toward expecting "one" outcome during uncertainty -- a negative one. This drags your brain from a fluid state into a configuration that is set up for failure.

In this case, increasing your optimism bias (e.g. by playing games that train you to look at the positives in a situation) may improve how much uncertainty you're able to tolerate. 

Raising your optimism bias to balance your negativity bias returns your brain to a more neutral state that anticipates both positive and negative outcomes more evenly. 

Like the tennis player floating from side to side, your brain assumes a more fluid stance, equally ready for any of a range of outcomes. 

This may explain why successful entrepreneurs tend to be strikingly optimistic. Nobel Laureate author of Thinking Fast and Slow, Daniel Kahneman, calls this "delusional optimism."

It is impossible to sail a venture into the unknown without uncertainty and to ride those tides of uncertainty without grasping at optimism -- no matter how delusional that optimism may be.