Lean-Agile development depends on a high grade of customer engagement. There can be different ways to engage a customer which is dependent on the solution which either can be General or Custom-Built.

A General solution is DESIGNED to be used by a large group of people whereas Custom built focuses on individual customers. General solutions developed must address the needs of a larger AUDIENCE. No single customer is an adequate PROXY for the whole market. (as per ScaledAgileFramework.com)

For custom-built solutions, the external customer is typically defining the solution with the support of Product and Solution Management. However, EVEN though the customer is leading the effort, it is critical to establish a collaborative approach to scope and prioritization. This fosters incremental learning and exhibits a willingness to adjust the course of action as needed. Active participation in PI planning, the solution demo, and selected SPECIFICATION workshops is required. This will often reveal inconsistencies in requirements and design assumptions, with potential contractual problems. This process should drive the customer and ARTs toward a more collaborative and incremental approach. (as per ScaledAgileFramework.com)

The success of Agile is mainly driven by Customer Engagement. Every communication with a customer give companies an opportunity to not only provide a great experience, but to collect visions that can be used to mend processes and provide an even better customer experience.