How do startup founders even come up with an idea thats profitable in the first place? I will not promote

yeah as the question says, Ive been wondering for a long time how the idea for the startup pops into people's heads, and how people further develop it into an actual business. I would like to have a startup of my own one day, and i started by thinking about the passions that I have, but none of them seem profitable or worthy enough to become a business. What directions should i take to brainstorm for some ideas?