Try to run 3 miles, with a lack of aerobic fitness, and the result will be unpleasant. But it's not just because of the underpowered aerobic system, or even a lack of significant muscle or tendon strength.
Try to tamp with your off hand, and see how that goes. Let's make it easier. Try drinking your coffee with your off hand. Notice how unsure you are, how odd this all feels. Perhaps you even need to keep your eyes focused on the mug, lest you miss your mouth altogether.
This is not a lack of strength, but coordination. Your muscles could do the task, if only your mind could get them working in a coordinated manner. You need practice, nothing more.
This is the specificity of skill acquisition, too often overlooked in favor of frivolous bullshit. Ancillary things are nice, in their place. But whatever it is you want to improve, you need to do. A lot. Their are neural pathways that need cleared of dense brush, so get your machete out, and hack away.