I remember hearing in a shiur from R’ Pesach Krohn that the gemara in Taanis on 29a (quoting the mishna) states, “Meshenichnas Av, m’maatin b’simcha”, when Av arrives, we reduce  the level of happiness. Note that it does not state that we shall eliminate happiness altogether and become sad, but rather that we just reduce our level of happiness.  As Jews with emuna, even when things seem to be going wrong, we must always remain happy.