not able to log in; if cookies is disabled in browser

I am not able to log in to admin  pages of my site  if  cookies  is  disabled in my browser
why it  happens so?
 
the section for authentication  in web.config is pasted bellow  
 <authentication mode="Forms">
            <forms name="sqlAuthCookie" loginUrl="~/Admin/MemberLogin.aspx" timeout="20" path="/" protection="All">
                <credentials passwordFormat="SHA1">
                </credentials>
            </forms>
        </authentication>
 
I cant also log in to http://forums.asp.net  if if  cookies  ...