When switching projects, it's essential to verify assumptions about existing code and its behavior, rather than relying on imagination or past experiences. This can help prevent mistakes like the one made by the author of libmongoc, who assumed that IPv6 support was already implemented correctly but didn't verify it. Additionally, it's crucial to test even ordinary features thoroughly, as bugs in these areas can be difficult to detect. The author also learned a valuable lesson about being disciplined when fixing bugs and minimizing risk, especially in patch releases. By adopting a more cautious approach, developers can reduce the likelihood of introducing new bugs while still making progress on their projects.