A bad product manager will always hoard information. This is a competitive field, and you can’t let others know your secrets. Don’t share any lessons learned, as they can only be used by others to create products that will compete with yours. Refuse to talk shop with other product managers — it’s a waste of time, after all, since it takes your focus off your product. Telling others how you do your job or what your experience is with product management is just a bad idea.
A good product manager will always share her knowledge. Realize that you have lessons to share but even more to learn. Know that you improve your own skills and expertise when you teach others. The vast majority of other product managers are not competing with you, so everyone benefits when knowledge is shared. Communicating your perspective helps you explicitly formulate your own beliefs, affirming good practices and making you question bad ones. It overall raises the level of discourse about product management and ultimately helps product managers and product development professionals do their jobs better and create better products, in turn helping any consumers of those products.