The title is a bit misleading because it makes it sound like we're talking about a scalar. Actually you can control both the length and the direction of the vector. The direction is probably the more critical.
That reminded me when a physicist once told me that in physics and life, Work = Force * Displacement.
There's a different way of thinking about effort that takes into account both direction and magnitude. What could you be doing right now that would make you $10,000 an hour? This way, you will focus on the right tasks, and the right intensity.
You're projecting the vector onto a plane. You still have to pick the right plane (I wouldn't have chosen this one, for example), but it does simplify things in that you only have to choose once.