In a developed ecosystem, even the predators and pests are providers and energy is not lost, just converted.
Little balls of caterpillar poo = little balls of fertilizer.
In this picture, the caterpillar eating our Pear tree is providing nutrients for the Sunflower that lives below it. My needs are only secondary and the fact that I would prefer to eat Pears than Sunflowers is irrelevant to that caterpillar. Even the accursed Slugs provide nutrition in their own way and I am probably least relevant to them as they go about their work.
We gardeners have to learn our role in the ecosystems we develop. We are the conscious, guiding, force that gives a garden its content and form but there are many other inhabitants who play out their role on a daily basis. Plants, pests, microbes, fungi and the whole gamut of life have been doing their thing since long before we got started and will do so long after we have gone. We have the ability to develop an overview of the ecosystem of the garden and the ability to think outside of the now but our plans must include knowledge of the relationships between all of the elements at play and our relationship with them.
Successful gardening acknowledges this and the gardener attempts to guide their charges to a balance that he or she envisions. We shape it to suit our preferences but we are only part of the action. Anything that goes against this thinking results in stress and anxiety.
I'm no gardening saint and still reflexively kill off bugs that I see eating my valuable food plants but I've left that particular caterpillar to go about its business because it taught me a valuable lesson today and now I get joy from observing the signs of its existence.