No matter what a team tells a young player in that situation, the kid will be disappointed, that's just a natural reaction. I couldn't find any quotes from Nieve, but I did find this by Purpura from 7/22...

"We tried to challenge Fernando to go down and work hard," Purpura said. "We know he will. We challenged him to work some late innings, come in the middle of an inning. He'll get a chance to close some games. He'll do some things that should help him when he comes back here to be hopefully a big part of our bullpen."

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