I realize when you use the word "period" it has a very definitive connotation. Quite honestly if you're trying to maximize your growth and productivity on a daily basis then the groundupSALES quote below is THAT definitive. Uncontrollable's are inevitable variations that we need to consider as we make decisions but that's where it should end. Worrying saps energy, focus, and time and we need as much energy, focus, and time to use on what we can control. I view this as one of the human minds biggest stumbling blocks.
Stop worrying. Start doing.