ما كل ما يتمنى المرء يدركه
A person does not attain everything he wishes for.
The line does not say that no wish is ever fulfilled. Rather, it denies the universal proposition that every wish is attained. At least some wished-for outcomes fail to occur.
This is salb al-ʿumūm (سلب عموم), negation of universality. It differs from ʿumūm al-salb (عموم سلب), which denies the predicate of every member of the class.
The placement and scope of “كل” matter because the same broad topic—wishes and attainment—can yield different logical claims.