There were some who doubted whether or not the crew of the U.S.S. Enterprise was ready for the universe or not. Yes, they were young; yes, life had not been exactly good to them. But what they have been through had made them strong, and yes, they have been through a lot:
…Loss…
Kirk had felt the loss of his father since the day he was born. It had affected nearly every aspect of his life; made it harder, more complicated. It was the loss of his life that allowed him to push himself to his limits and beyond to protect the lives of those around him.
…Loneliness…
Spock had been forced to be alienated for his entire childhood for his dual nature. If it was not for that, he would have likely joined the Vulcan Science Academy and died with the rest of his home planet. It was his alienation at such an early age that drove him to be loyal.
…Abandonment…
Bones had wandered aimlessly after his wife left him. For weeks he just wandered, not goal, no destination in mind, until the day he joined Starfleet. It was the abandonment from the woman he loved that drove him to strengthen the bonds of friendship and others like never before.
…Humiliation…
Scotty had been humiliated the day that Archer's prized beagle did not reappear. He had been humiliated the day that he was exiled to Delta Vega. Because of this great humiliation, he wouldn't put something up in the real amount of time it would take, and he would never put something below himself.
…Indignity…
To say that some of the stuff Uhura had been put through because of her gender and ethnic origins was an indignity would be an understatement. Though racism and sexism had mostly faded into history, there was still the occasional backwards fanatic. Because of it, she treated others with dignity.
…Fear…
Sulu had feared for his life when he fell of that drill. He came to the realization that he had always been a coward before then when the transporter finally caught him a Kirk. It was then, when lying on the transporter floor, that he would finally face his fear, regardless of its strength.
…Frustration…
When people gave Chekov that look, that look that told him that they underestimated him and they wouldn't let him try because of that, it frustrated him. Because of his youth and the comparative inexperience it, people did not want to give him the chance. It was because of this that he would try not to underestimate others.
The question wasn't of whether or not the crew of the U.S.S. Enterprise was ready for the universe; it was whether or not the universe was ready for the crew of the U.S.S. Enterprise.
Author's Notes: Special shout outs to Protector of Canon2 for suggesting frustration for Chekov, which led to his own section.