By completing this chapter, you should be able to design and reason about multi-stage pipelines. You should understand $match, $project, $set, $unwind, $group, $sort, $limit, $map, $filter, $reduce, conditional expressions, $lookup, $unionWith, date expressions, conversion, $facet, $bucket, set operations, window functions, $graphLookup, $count, $out, $merge, and performance analysis.

Before moving forward, build a report that calculates delivered revenue per customer, joins customer names and cities, ranks customers, and returns the top three. Define discount handling, avoid duplicating revenue during joins, handle missing customers, and verify the result manually.

You are ready when you can explain why each stage belongs at that point, what document shape it produces, how invalid data affects the result, and what evidence supports your performance decisions.