Some of the most successful companies in YC history formed when founders confronted a real world issue. Airbnb began in 2007 when Brian Chesky and Joe Gebbia were having trouble paying rent, so they bought a few air mattresses and charged people \(\$ 80\) per night to sleep on them during a busy convention in San Francisco. In 2010 , Patrick and John Collison began working on the side project that would later become Stripe after Patrick became fed up with how hard it was to accept financial payments on the internet. The founders of Gusto started their company because they were frustrated by the inefficiencies in payroll for small businesses.
You don't necessarily need to start with a specific idea. Simply take a look at your own life, identify a problem, and then build a solution. You might be surprised how many others have the same problem too.