For a long time, the plant seems small, so you decide not to worry about cutting it back until it covers half the pond. The answer is, One day. The water lily will cover half the pond on the 29th day, leaving you only 24 hours before it chokes out the life in your pond. The behavior in all of these instances seems counterintuitive. We generally expect things to follow linear patterns of growth.
Linear growth occurs whenever a factor expands by a constant amount each time period.
But positive feedback causes a factor to expand by a constant percentage each time period. Then, although the underlying growth process hasn t changed at all, an explosion seems to occur. The 34th doubling would actually add another 3,400 miles to the napkin s thickness, as much as has accumulated throughout all past history. To understand this behavior, it is useful to show a causal loop diagram the underlying loop structure. If you have time, ask participants to work together in small groups to draw the simplest possible diagram that explains the growth in the napkin s thickness.