And although it seems like a good idea to have someone around for several years to size him up carefully before granting him tenure, there are great costs. It destroys collegiality. I cannot be perfectly frank or fully friends with someone whom I am going to judge or who is going to judge me at a later date. When I was considering spending sabbatical leave in the US, I ruled out certain East-coast universities because they were reported to be riven by disputes over tenure, and I wanted to be somewhere where I could be friends with everyone. Although granting tenure to an outsider on appointment at a young age is risky, it costs far less than deferring a decision until it is much more difficult to take and will do much less good.
Academic appointments are risky.
Academics go off, get stale, run to seed, fail in innumerable ways to fulfill their early promise. But not to run the risk is to forgo the chance of success. I did not get the Fellowship, but got to Princeton on another, followed up my hunch, and in due course published the result. I have not succeeded in persuading the majority of my colleagues of the validity of my argument, but some are convinced, and scarcely a year goes by without some further discussion being published. To demand certain success in appointing academics is to diminish the chances of getting it.