Why can't lseek the STDIN_FILENO?

Hi community,
I am testing the lseek & write & read, and I write the code like this:

/*
    lseek_test.c
        Test the lseek
    Wen Yi
*/
#include <unistd.h&gt;
#include <fcntl.h&gt;
int main()
{
&nbsp;&nbsp; &nbsp;int fd = 0;
&nbsp;&nbsp; &nbsp;char buffer[16] = {};
&nbsp;&nbsp; &nbsp;write(STDIN_FILENO, "Hello world\n", sizeof("Hello world\n"));
&nbsp;&nbsp; &nbsp;lseek(STDIN_FILENO, 0, SEEK_SET);
&nbsp;&nbsp; &nbsp;read(STDIN_FILENO, buffer, sizeof(buffer));
&nbsp;&nbsp; &nbsp;write(STDIN_FILENO, buffer, sizeof(buffer));
&nbsp;&nbsp; &nbsp;return 0;
}

And I run the program ("Something Input" is my input content)

[beginnerc(at)bogon 学习 C语言]$ gcc lseek_test.c
[beginnerc(at)bogon 学习 C语言]$ ./a.out
Hello world
Something Input
Something Input
[beginnerc(at)bogon 学习 C语言]$

I really don't know, why the buffer's content not be "Hello world\n"? (I use the lseek to move the cursor to the beginning region)

Can someone give me some advice?
Thanks in advance!

Yours,
Wen Yi