Effective leaders understand the difference between being like a thermometer and a thermostat. A thermometer goes with the flow. If things are good, they are in a good mood, have a good attitude and see the good. If things are bad, their demeanor, attitude and outlook turn bad.
A thermostat sets the temperature. No matter what is going on around them, a thermostat's internal mood is constant. Through the sheer force of their personality, their leadership methods or their attitude, they set the mood of the entire environment and everyone/everything in it.
Of course, being a thermostat can be a good thing or a bad thing. Some people's internal mood is constantly set on negative. Even in the face of loads of positive, they seek out and find that speck of negative.
Step 1: Learn how to be the thermostat, not the thermometer.
Step 2: Set your internal thermostat to positive, constructive, and encouraging.