Keep painting the same horizontal line on a canvas and soon enough paint will accumulate and begin to drip down. Once a drip begins to roll, it’s not clear how far it will roll.
The metaphor created by Kent Beck describes a generalist who acquires specialised knowledge when required and for as deep as is necessary.
Most coaches are technical specialists who like to paint in vertical lines. Going deep into a skill set on the assumption that it will be necessary.
The problem comes when a specialist needs to generalise. Because the paint runs in a vertical line when it comes to painting a horizontal line there is little or no paint to take across.
Parents, coaches, and teachers when it comes to kids be careful where you put the paint.