One feature of religion a lot of secular people do not understand is that, although religion can make one feel guilty at times, it also prevents one from feeling guilty about trivial matters. Secular people think that by avoiding religion they avoid feeling guilt, but often they end up overwhelmed by guilt, because they attribute to all their mundane earthly projects an inflated moral significance.
One of the best examples is creative or intellectual work. Or career advancement. If I publish a blog post that everyone hates, or if I fail to get a promotion, or one of my silly hypotheses turns out to be wildly wrong, I really don't care because none of these things matter too much for better or worse. I believe they constitute a meaningful and honorable calling, and my dedication to this calling I believe to be Good in the long-run, in a way that matters. But failure on any particular project causes me no shame, because it reflects no sin. Shortcomings on such earthly diversions simply never take a moral tone for me, because they are orthogonal to morality as I know it with the help of my religious tradition. For a good Christian, creative and intellectual work is beyond Good and Evil. But for people who don't believe in sin, for people who think they can simply free themselves from guilt by ignoring it, then a failed writing project or a career setback can feel like a moral failure. It can, and often does, produce feelings of shame, for instance.
If one of my personal intellectual efforts fails, I would never think to bring this to the confessional! Which means I would never experience compunction or shame about it. For the arrogant, modern, secular type who thinks himself too good for the confessional, some little practical shortcoming that hurts nobody can affect their body like a real sin would affect mine. Not only does secular guilt accumulate more heavily (given the frequency of practical shortcomings), but the secular person suffers from guilt far longer than the Catholic, for the secular person admits no mechanism of absolution. This is one of the least understood reasons why modern secular minds are sometimes unable to create, despite deep yearnings to create. And why — when they do create — it is often superficial, instrumental, and ephemeral. They conflate their earthly, mental creations with an eternal, ethical plane they neurotically deny and desire. Finding their finite abilities not up to the task, they decide never to begin, or sell themselves short.