To build anything non-trivial you really need both, but the frontend is generally easier to start out with and get enough visual feedback to motivate you to go

To build anything non-trivial you really need both, but the frontend is generally easier to start out with and get enough visual feedback to motivate you to go deeper and deeper into the stack. The reverse is far more difficult for most people. As you go deeper and get exposed to more concepts, it's only natural to specialize in either backend or frontend.