Nothing matters in the end. But we will not be here after the end, so the fact that nothing matters in the end is irrelevant to now. What we do right now could matter in 20 years time, or 5 minutes time. So what you do right now does matter, because it determines how your life will be while you're here. Like, if you cut your own genitals off, it doesn't matter in the end. But it affects the rest of your life.