Let $k$ be a field and $N$ a finite group. Let $M$ be a projective indecomposable $kN$-module. Since the algebra $kN$ is symmetric, it follows that the top and bottom composition factors of $M$ are isomorphic. In particular, there is a nonzero endomorphism of $M$ sending $M$ onto the socle $\operatorname{soc}(M)$.

I cannot see the connection here. How does being symmetric implies composition factors? Any help would be appreciated!