All this is to serve to create some desired forms of strokes. No need to torment ourselves by sweating over its "mystery". Some mature western painters likely do that too. For instance, in the painting below by Anders Zorn (one of my most favorite painters), strokes of many different shapes must have been obtained by manipulating the brush.
By the way, Zorn used round brushes (most western painters use flat brushes) that resemble Chinese brushes.
Inconvenient for me to load up a picture with my iPad. Here is a good source link for this painting: https://www.flickr.com/photos/gandalfsgallery/7076039745/in/photostream/lightbox/
