What: Letting an edge dissolve into its surroundings (shadow or background) instead of outlining it with a hard line.
Why: Lost edges guide the eye toward the focal point and give depth and softness.
How: In shadow or background areas, let the form merge gradually with no outline.
Common mistake: Outlining everything with a hard line so the work looks flat like a colouring book.
Exercise: Draw a portrait and let one side dissolve into shadow with a lost edge.