You only live once (YOLO)?

I have heard this expression before but I heard it again on an escalator goings toward my work place, two guys were talking on either side of my escalator when one shouted you only live once right and the wheels in my brain started churning. My daughter also says sometimes like this and I don’t know if it is really true that we have only one life to live. Who started this thing and who keeps on perpetuating it? How do we know that that we have only life to live and how did we come to this conclusion. If for example we have only one life to live, do we go all crazy and do stupid things or do we live morally and help other people and do good deeds. If this is the only life we are going to live, do we then not fear any retribution for our sins and shall we are selfish and live our life the way we want to live since it is the only life we know? The truth is we know that there will be a life after death (and I know not everyone will agree with me on this) since if there is no life after death then we should all assume that the sinners will go scot free and whatever they have done in this world will not face any retribution or justice for the people who have been faulted by their actions. Yes in this world, we are here for a purpose and if we succeed in being a good human being, we should expect justice in the afterlife otherwise we are no less animals who can do whatever they want without getting punished for our sins. You may only live once in this world and that is all we know for now but after this life, we will surely face our sins and get ready for any rewards or punishments for our actions. As I firmly believe that there is life after death.