They should be challenging because if you overcome them you can keep on gong and try something even more challenging intill nothing on your list of goals.

They tightly controlled trade and held a monopoly to obsidian trade. That way they coud keep others from making weapons.

remember the sabbath and keep it holy. Exodus 20: 8

more challenging

Cheetahs are wild animals that have specific needs and instincts which makes challenging to keep as a pet but with the right needs meet them you can keep them as pets