Why was Chips startled when Ralston gave him a soft reminder to think about retirement?

When Ralston suggests that Chips should retire, it's a total surprise. Chips has never liked Ralston. He feels that he's more of a hyper-efficient bureaucrat than a teacher, certainly not a molder of boys into men. He's obsessed with increasing the number of rich pupils attending the school, which has led to something of a snob culture developing at Brookfield. Chips is also disillusioned about the academic changes that Ralston's introduced, especially the new way of pronouncing Latin. Ralston, for his part, looks upon Chips as a bit of an old dinosaur, an unwelcome reminder of the school's past. Chips's eccentricities, such as his tatty old master's gown, are also a source of irritation.
So why is Chips surprised when Ralston suggests he should retire? Over the years Chips has shown outward loyalty to Ralston despite his personal animosity towards him and his misgivings about the school's change of direction. He's witnessed firsthand the ruthlessness with which Ralston deals with masters who get in his way. But Chips thought it would be different for him. He thought that his age and seniority would somehow protect him. Chips is hugely popular in the school, with boys and masters alike, so he also thought that his popularity would protect him.