Truth is reality. Reality can be painful without acceptance, resignation. When we are angry at our circumstances, or at some injustice, or at some hurt, then we feel the pain. We are not willing to accept the reality. We are fighting our fate. This lack of resignation always causes pain. Truth is painful.
But many of us are clever. And are also wise. We accept the play of karma, because we believe in its justice. We don't blame anyone for the troubles in our life. We embrace them with grace and fight them with pace. When that happens, truth is not painful.