In an economy, resources are limited. However, people's wants are infinite. So when the limited resources meet the infinite wants. This would cause scarcity.
Sacrcity is a state in which we do not have enough resources to satisfy ALL out wants.
Scarcity is a relative concept: a resource is scare only if its available quantity is not sufficient all our wants for it.
DO NOT THINK that a resources in little supply must be scare.