On a roll
If a person is "on a roll," that person has good momentum in what he or she is doing.
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DefinitionYour turn
There were be two episodes about happiness: today’s and Thursday’s. Why? Because Jeff was on a roll! He had good momentum. He had a lot of content, a lot of ideas, he was writing so fast and so much, that he wanted to write two episodes about the topic. He was on a roll.