Unfortunately, most of us only think about the “why” after we do something self-diminishing, not before. But, to change undermining beliefs and habits, we will need to think about them before undermining ourselves. In fact, as we shall see, we need to completely change our thinking in some areas, thus changing our brains.
First, if the question assuming that "ultimate meaning" can only exist in a context of some kind of afterlife (eternal or otherwise), then the deck is stacked, and no answer apart from that would be conceivable. The issue ultimately relates not to the afterlife at all, but to what meaning and purpose people come to think about their own lives and the lives of others.