Insufficient research. Without conducting the user and market research to fully understand the needs of potential buyers, it can be challenging to design a product that will be successful in the marketplace.
Focusing too much on aesthetics. Putting too much focus on aesthetics in the design process is a common mistake that can sacrifice functionality if equal attention is not paid to usability and product performance.
Not considering the manufacturing process. Research the manufacturing process early in the product design process to better inform your production plans and costs.