In Night at the Museum, when Larry exits the Security Room, why does Cecil mean "Oh yes, he's the one" after Reginald asks "You really think he's the one?". What did they mean? What were they talking about?
Well, Cecil and his gang had made their "retirement plan" quite a long time ago. They knew about the powers of the Tablet of Akhmenrah but they wanted a skapegoat/patsy/fallguy to put all the blame of stealing the tablet on.
It is shown by the end of the movie that Cecil and his gang were wicked and planning about the robbery the whole time. And they found that easy mark in Larry.
The coversation between Cecil and Reginald shows this same thing. Reginald was a bit skeptic as whether Larry would be the right choice, for which Cecil replies the same.
Since Larry was in a bad state at that time - divorce, jobless, staying away from his kid, Cecil and his gang found him to be the perfect fit for the bait.