Onur Cobanli explains:
Solo designers risk creating solutions that only make sense in their own minds. Working with diverse perspectives ensures designs work for actual users. Multiple viewpoints prevent blind spots (and catch problems early). That said, who cares, just do your thing to begin with, and then you can collaborate. But if there is an opportunity seek feedback, asking people feedback and their preferences is already designing with others, they don't have to actually sit down with you to design, they don't need to be there at the final designing step.