What do you consider the most important phases of a product's lifecycle?

I think a product deployment starts with ideation.  I would crowdsource and get multiple inputs for product content to ensure the deliverable is valuable to our customers.  Then product development, which is tested iteratively by internal quality assurance and beta customers in a sandbox test environment.  Prior to deployment, I would again get feedback and iterate based on the beta customers experience.  During deployment, I would ensure that communications are delivered to customers and internal stakeholders, complete with documentation in multiple areas, including reference documents in knowledge base articles and customer forums.  During support, I would provide feedback on the most impactful areas of the product and those that generate the most time and energy to support.  This would result in product improvements and enhancements during the mature phase.  Once ready to sunset, I would develop a transition plan for our customers to the replacement product or service, mapping the old and new workflows and highlighting the changes that may be required to business processes with the new product.  Upon retirement, I would provide a complete lesson learned document to the new product service owners.