Why is it necessary to use "result as T" in the return of a generic method?

Question

Consider the following method:

private handleError<T> (operation = 'operation', result?: T) {
    return (error: any): Observable<T> => {
        this.log(`${operation} failed: ${error.message}`);
        return of(result as T);
    };
}

whereas the implementation of a generic type implies a return of the same generic type T, why the need to use the result as T, whereas result will always be the type T?

return of(result as T);