It is generally accepted assumption that every resources cannot be enough. But this is a different issue from what human nature is. No matter what human nature is, if the resource is scare, they compete, which means they want to have the resource more and more until they think it is enough. But since the first assumption is that every resources cannot be enough, they cannot stop competing.
This is the order of the logic.
1. Every resources is limited.
2-a. Human nature is that people want to have every resource endlessly.
2-b. Human nature is that people want to have every resource until their basic needs are satisfied. ( This basic needs cannot be satisfied, because assumption 1 implies it. But for some resources, such as air, people can feel satisfied. )
3. People compete.
Whatever we choose between 2-a and 2-b, people compete. It is not because of human nature, but because of the resource.
Some people say that the reason why people compete is human nature. But I don't think their logic is impregnable. It is still controversial whether people has unlimited desire or not. If any philosopher or psychologist has proved it, I want to read the book. But I have never heard it yet.
In other words, if someone want to talk about human nature, they should reconsider the first assumption whether the resource is enough or not in the specific case.