I don't want to sound like a smart a** because this is a real learning, but also may help you get better responses. One of the main things I have learned is how to ask better questions. Asking what was the biggest lesson is like asking which part of the fire is hottest. They are all big lessons. There are so many takeaways that unlock deal flow, network, contacts, deal structure, etc that it is literally impossible to pin one down as the most important As we have worked through different situations, had strategy sessions around deal structure, deal flow, due diligence, etc.... the lessons are endless, as they should be

Answering questions better too. Most people say/write too much, answer the question they wanted to be asked or respond respond with questions of their own without moving the topic forward. Searching is mostly about communication and most people are poor communicators. Hone this skill and it will pay dividends beyond the search.