Complex sentence: In the early 1970s Theodore Levitt and others at Harvard argued that instead of producing products then trying to sell them to the customer, businesses should start with the customer, find out what they wanted, and then produce it for them.
Split into simpler sentences: In the early 1970s Theodore Levitt and others at Harvard argued that the sales orientation had things backward. They claimed that instead of producing products then trying to sell them to the customer, businesses should start with the customer, find out what they wanted, and then produce it for them.