Initially, lack of battle experience.
Katniss everdeen. her trick with the berries nearly ruined the capitals games.
The greatest challenge to overcome in Arthur Miller's Death of a salesman would be transitioning to the constant flow of flashbacks.
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defeating the greatest military power in the world
Yes you can overcome a challenge, or you could use: conquer, defeat, master, prevail against (or over) ,surmount, triumph over,
he fight them
Hannah does not overcome any challenges, rather she fails to overcome them. Like the challenge of deciding to live or die and the challenge to overcome the nasty rumors she's faced with.
Challenge accepted.
The biggest challenge for him is not sounding horrible and repetitive. It is a challenge he still hasn't overcome.
Fear is a challenge because the person is not going to want to do it since they are scared. If you can overcome the fear then you have won that challenge.
Not enough rainfall
The will to get things done