You will often see effects in one layer surface as causes in another layer. For example, if demand on one layer exceeds its capacity, then that layer’s performance degrades. It responds slowly or not at all. Slow response is actually worse than no response. When that happens, the slowdown in one layer can trigger a cascading failure in another layer. This can make it difficult to separate capacity questions from stability questions. During the launch of the retail site described in Chapter 7, Case Study: Trampled by Your Own Customers, the team experienced a severe capacity problem that led directly to a stability problem.