shediv on "wp_mail and @wp_mail difference"

Hi,

I am new to WordPress development
I was trying to send attachment with wp_mail but what i noticed is that when i try
wp_mail($to, $subject, $message, $headers,$mail_attachment);

mail goes but without attachment

And when i do
@wp_mail($to, $subject, $message, $headers,$mail_attachment);

attachment goes...

Any one can tell me why so..???