Final answer:
Beethoven detailed his musical composition process in sketchbooks, which provide insight into his artistic struggles and methodology.
Step-by-step explanation:
We have a record of Beethoven's struggle with his musical material because he showed his workflow in musical sketchbooks. Unlike the character Aylmer from our reference, who documented each experiment in a folio, Beethoven used sketchbooks to intricately outline the development of his symphonies, quartets, and other compositions. These sketchbooks are a window into Beethoven's creative process and illustrate how meticulously he crafted and revised his musical ideas until they met his rigorous standards.