And if you change your example only slightly, you can break again most-people's mental-model of pointers:

    #include <stdio.h>

    void fn(char *s) {
        printf("[%s]\n", s);
    }

    int main() {
        char *s;
        s = "hello world";

        fn(s);

        return 0;
    }

And yet again:

    #include <stdio.h>

    void fn(int s) {
        printf("[%s]\n", (char *)s);
    }

    int main() {
        char *s;
        s = "hello world";

        fn((int)s);

        return 0;
    }

And back to a single char:

    #include <stdio.h>

    void fn(char *c) {
        printf("[%c]\n", *c);
    }

    int main() {
        char c = 'a';

        fn(&c);

        return 0;
    }

The ugly and evil way:

    #include <stdio.h>

    void fn(char *c) {
        printf("[%c]\n", c);
    }

    int main() {
        int c = 'a';

        fn((char *)c);

        return 0;
    }

And the obvious way:

    #include <stdio.h>

    void fn(char c) {
        printf("[%c]\n", c);
    }

    int main() {
        char c = 'a';

        fn(c);

        return 0;
    }

It is not difficult to see why most people find pointers in C confusing.