This single image from Nicky Epstein's 2008 book, "Knitting on Top of the World" changed my life. Sweater making was instantly made easy (but time consuming in fingering weight) and so were all other articles of clothing.
A rectangle becomes a tube, which becomes a sleeve. This simple logic made everything come into focus. I could not just imagine skirts and sweaters, but also pants and shorts.
I hope this visual helps you on your journey. There are so many pearls of wisdom in this book. Many methods to strengthen your skill set and spark your imagination as to what else can become possible.