I learned for example that plants form partnerships with particular bacteria and fungi. The bacteria and fungi feed on carbohydrates manufactured by the plant (through photosynthesis) and exuded by its roots. In return, their excreta provide nitrogen and other nutrients to feed the plant, and they coat its roots in a protective film. Individual plants actually control which organisms they attract, according to their needs!
Then the keen gardener comes along with crude chemical fertilisers and knocks the whole system out of balance. No longer reliant on the microbes, plants grow fat on the readily available nitrates poured into the ground. The microbes consequently die out. From then on, the gardener has to keep feeding the plants artificially or they won't thrive – remember, the microbes are gone.
When the microbes leave, the larger soil organisms such as earthworms leave, to the great detriment of soil structure and soil health. As the soil structure degrades, more and more of the synthetic fertiliser goes straight through into the groundwater, where it becomes an environmental pollutant.
(As an aside: ever wondered why we have toxic algal blooms in our rivers every summer? Yeah, right, it's 'natural'.)
With unbalanced nutrition, the plant is more susceptible to pest and disease attack. What to do? Spray it with various '-icides' to rectify the problem. Trouble is, they make the soil an even less hospitable environment for its natural inhabitants.
In other words, a quick fix solution has put the gardener on a chemical tread mill. From now on, gardening will be more labour intensive and expensive. It will rely on inputs which can't be manufactured within the garden, but are products of the petrochemical industry.
To my mind, it's just one more example of how organic methods are not just more effective than chemical methods, but easier and cheaper.