I can’t get the following statement, why would arithmetic mean be a better instrument than the geometric mean? Should not the geometric mean be more accurate!

_ “Compared with the geometric mean return, the arithmetic mean return is consistent with the assumptions of single period models, such as the CAPM.” _

Its simple. Understand the material rather than memorize the material. Some stuff still forgets as the breadth is huge, but I try to retain the core material rather than the obscure.