为什么在c中使用fork进行两次父打印？

#include <stdio.h>
#include <unistd.h>

int main() {
    pid_t pid;

    pid = fork();

    if (pid == 0) {
        // 子进程
        printf("This is child process\n");
    } else if (pid > 0) {
        // 父进程
        printf("This is parent process\n");
    } else {
        // fork失败
        printf("Fork failed\n");
    }

    return 0;
}

This is parent process
This is child process