Hiring a Human-Computer Interaction (HCI) developer is crucial for creating user-friendly interfaces that enhance user experience. They combine design, behavioral sciences, and computer science to make your product intuitive, efficient, and enjoyable. They conduct user research, design interactive systems, and evaluate the system's effectiveness. This leads to higher user satisfaction, increased user engagement, and potentially greater customer retention and revenue. Their skills can make the difference between a product's success or failure in the market.