This is not a slackers mandate - far from it . Underpinning wu wei is the fundamental principle that there is a natural order and flow to everything. To be aware of this flow, we all need to be as sensitive as possible, or else any action that is not wu wei will either have the wrong outcome or not work at all.
So we need to be sensitive and receptive, and act spontaneously in a non-interfering way. When we listen to our inner voice and allow ourselves to learn and grow naturally, our actions become effective with the minimum of effort. The modern saying is "go with the flow". The Chinese philosopher Chuang Tzu called it "Purposeless Wandering."
To let go of our relentless clinging on to controls and measures can be terrifying. It goes against everything our modern society and many of the most basic assumptions of life. But allowing the natural flow of things to take care of themselves, and acting fearlessly in accordance with your physical and mental instincts produces breathtaking synchronicity and greatly reduces the level of stress.
If you want a safe go at it, hide all the clocks and watches in your house, and spend the day without a plan. You'll be surprised what gets done - and what doesn't get done.... and also how un-stressed you are at the end.