Growing up, I was always told to save water and energy because "the Earth's resources are finite, and we only have one Earth." This always struck me as slightly wrong, at the same time, it so simple and obvious that it's hard to refute.
I think it's a very common sentiment in Germany and part of the culture. The core notion is that at some point, we will use the last liter of fresh water or mine the last piece of iron ore on Earth.
Reactions to depend on how one views human capabilities and our interactions with the natural world:
Responses can range from advocating managed growth (becoming more efficient) to degrowth or even believing humans shouldn't exist at all or that they are fundamentally a strain on the natural world. This dovetails nicely with some deep seated Chrisitan beliefs.
If you believe humans should flourish and accept the premise of finite resources, the response often ends up looking like "we will conquer space and mine resources from asteroids and other celestial bodies before we finish earth's resources".
I believe the statement itself is fundamentally flawed.
If we consider the physical laws of nature, outside of atomic fission or fusion, matter is never lost, only transformed. Energy transitions from lower entropy forms to higher entropy forms, but Earth is continuously bathed in vast amounts of energy from the massive fusion reactor in the sky and receives kinetic energy through interactions with other celestial bodies. On balance, it will be a long before our energy consumption matches the amount of free energy we get every day.
If we take a historical perspective, we realise how narrow the concept that the Earth is finite is. When we think about finite resources, we always consider resources relevant to our current technological capabilities. A Roman philosopher might have agreed that eventually, we would use up the last tree, harvest all the fields, and exhaust all bronze and marble. But to us, today this would seem like a ridicious consideration.
Humanity has consistently discovered entirely new resources and innovative ways to use existing ones more effectively. Romans saw coal as marginally useful — good for writing or as makeup — but during the Industrial Revolution, we harnessed coal as a powerful energy source for applications unimaginable. In antiquity, large portions of the population had to work the fields to sustain society. Today we require far fewer farmers yet produce more than ten times the food on the same plot of land.
"The Earth's resources are finite, and we only have one Earth," assumes that our current technological level represents the pinnacle of human progress. It implies a fixed usage of natural resources, humanity having to manage an ever-diminishing budget.
Human history shows the opposite: we find innovative ways to utilize new natural resources. We should anticipate the discovery of entirely new resources or novel uses for existing ones.
In reality, Earth isn't finite—as long as we keep innovating.