People who try to be clever for the sake of being clever are

为了变得聪明而尝试变得聪明的人绝对不聪明.
People(主语） who try to be clever for the sake of being clever （定语）are anything but.（表语）
再问： sake此处是目的的意思吗
再答： 是的。for the sake of 为。。。的目的而。。。。