Mae West once said, "Too much of a good thing is wonderful." Today's chief marketing officers would hardly agree. McKinsey's marketing and sales practice recently spoke with more than 40 CMOs from a range of companies around the globe. Their biggest concern, they told us, is that an explosion of customer segments, products, media vehicles, and distribution channels has made marketing more complex, more costly, and less effective.

Evidence of the new proliferation lies all around us. Consider the growing fragmentation of customer segments. Modern society is at once more multicultural, because of immigration, and more divided, because income groups have polarized into rich and poor. Both trends create additional and more distinct customer segments. At the same time, intense competition and hunger for growth have pushed, and supply chain innovations have allowed, today's companies to target ever more demanding customers within ever smaller segments. The product and service options available to customers of consumer industries from packaged goods to financial services have therefore doubled or even tripled.

As sub-brands and line extensions multiply, so do the messages and the media required to sell them. Twenty years ago, big companies used one advertising spot on three television networks to...