Can you please explain how and why with bipolar disorder have a hard time controlling their emotions?

By definition: Bipolar disorder is a condition whose very definition is that emotional highs and lows are both extreme and cyclic. Moods in bipolar are unusually far outside control by one's rational mind. This is a phenomenon rooted in how genetic influence on the brain, probably of nerve cells themselves: they fire in mutually-reinforcing clusters more readily than normal (mania) or less (depression).