What was Robert's biggest regret with Nook?

Robert names the cause of the downfall as the number of hidden costs and profitability issues — and the deeper problem that he "never thought that we'd work in a field that I had no expertise in, in a market I had no expertise in, in a language that I'm like only semi comfortable speaking and working in a professional setting in." Despite that, he looks back fondly because Nook brought lots of jobs and upskilled a team he's still proud of. His regret is the timing: "My biggest regret was probably not pivoting sooner."