inherent
Naturally built-in and basic to something from the start.
Inherent means naturally existing as a basic, essential part of something. When a quality is inherent, it's built in from the start, not added later or learned.
A dolphin's ability to swim is inherent: dolphins are born able to move through water. Your need for food and sleep is inherent to being human. These aren't things you develop or acquire; they're fundamental parts of what you are.
The word often appears when people discuss what naturally belongs to something versus what comes from outside. A triangle inherently has three sides (that's what makes it a triangle), but the color you draw it in isn't inherent. The challenge of climbing a mountain is inherent to the activity itself, while the weather you encounter on a particular day isn't.
People sometimes debate what qualities are truly inherent. Are humans inherently curious, or do we learn curiosity? Is bravery inherent to some people, or can anyone develop it? These questions matter because if something is inherent, changing it becomes much harder.
When you say a problem has inherent difficulties, you mean the challenges are part of the problem's basic nature, not just obstacles that happened to appear. Understanding what's inherent helps you recognize what you're actually dealing with, rather than what merely seems to be there.