"Newton's second law of motion, F = ma, is the soul of classical mechanics. Like other souls, it is insubstantial. The right-hand side is the product of two terms with profound meanings. ...The left-hand side, on the other hand, has no independent meaning."Now, who could be better to explain this than a parent with small kids? Applying too little force to an object, toy, flowerpot or big sister, is meaningless since it wont overcome friction or otherwise create any meaningful acceleration. Applying lots of force might be fun since the object might break or accelerate a lot or even both. But its risky too since you might get hurt in the process. Small kids experiment with force all the time. Eventually, as Wilczek indicates, they finally learn:
"when we hold up a weight— we definitely feel we are doing something, even though no mechanical work is performed. Force is an abstraction of this sensory experience of exertion."But its more than that, after having grown-up and fine tuned our nervous system, we actually continously feel with quite some precision the tension in our muscles, and we're thereby able to fine tune the force we are applying. We are able to handle objects without much consideration but yet almost always applying just about the right amount of force. Force as an abstraction seems very tightly linked to our "sensory experience of exertion". This might just as well explain the natural use of force in classical mechanics.
(Wilczek mentioning of exertion seems to refer to what you feel when the work the muscle have to do even to hold a static force [see his description of this process] begins to eat away the available energy resources in the muscle. Something I guess is quite different from the ability to precisely weigh objects.)