Bob warned me that THE gun on the top shelf of the cupboard was loaded. The phrase on the top shelf of the cupboard identifies the specific gun. Use THE when the context or situation makes the noun's identity clear. Please, don't slam THE door when you leave. Both the speaker and the listener know which door is meant.
Butterflies are frequently the pursuit of collectors.
The butterflies are frequently the pursuit of collectors. In some parts of the world, palm trees are the most commonly grown tree. In some parts of the world, the palm trees are the most commonly grown tree.