Statelessness absolutely does occur today, it is very possible. There is a good podcast called the Paperless People Podcast that goes more in-depth on this topic, but usually the way that people become stateless is through civil unrest and migration. For example, if a government chooses to disenfranchise a certain ethnic group, and then that ethnic group in turn decides to flee the country that disenfranchises them, they become stateless, because their country of origin won't validate their existence with another country. The Rohingya are one such case. People can also be born stateless, and usually this happens when a baby is born to displaced or stateless parents, such as in a refugee camp or on a boat in international waters. Not all countries grant citizenship based on being born in that country, and in such cases if the parents cannot validate their own citizenship then they will not have citizenship to pass on to the child.