Or, in this most recent case, two things.
The first is short-term and hardly serious. After taking a foul ball off his mitt in Wednesday evening's 4-2 win against the Mariners, Jorge Posada rested on Thursday with a bruise on the inside of his left thumb. Francisco Cervelli started in his place -- though according to manager Joe Girardi, Posada was available to pinch-hit or even catch, if needed.
"I was planning on giving him one of the next two days off," Girardi said. "So with that being said, it makes sense to give him today off."
It may be Cervelli's last start for some time. Pending rain, regular backup Jose Molina was scheduled to begin a rehab assignment Thursday evening with Triple-A Scranton/Wilkes-Barre. Rehabbing his strained left quad for the second time, Molina will catch five innings in back-to-back games, take one day off and then catch seven innings in back-to-back games.
At that point, he will be ready to rejoin the Yankees -- likely in Minnesota next week.
And although Girardi said the Yankees have not yet begun discussing what to do with Cervelli once Molina returns, it's unlikely that they would carry three catchers.
"We'll cross that bridge when it comes," Girardi said. "Our roster has one infielder and has a couple extra outfielders, but we'll cross that bridge when it comes."
Though Cervelli has shown extraordinary growth in his first extended stint in the big leagues, he is still just 23 years old and would presumably benefit more from playing every day in Triple-A than from catching sporadically in the Majors. The Yankees, meanwhile, are paying Molina well -- more than $2 million this season -- to be their backup.
Having him compete for playing time would seem counterproductive, even if Cervelli is the team's catcher of the future -- a tag he seems to have earned over the past two months.
"I think the way he's progressed is he has a better understanding of what our pitchers want to do," Girardi said. "I think he's comfortable catching our pitchers now. It's not so easy. I think as a player, that's the hardest position to learn. It's the hardest position to be a young player."
Anthony DiComo is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.