Hansen's judgment has been impeccable to date, his eye for talent is obviously keen. He is credible and therefore his conviction persuasive.
He is also selling a vision for which there are many potential buyers.
Remember the first Lions test in 2005? Or the World Cup quarter-final in 2007, or pretty much the whole of the 2008 season - Williams was untouchable, a rare mix of brutality, athleticism and mobility: the core skills all buffed and shiny laid out alongside a neat and eccentric range of extras. Memories nurture belief - brew hope that what Williams was once, he can be again.
Maybe. But faith can be so easily punctured by empirical evidence and Williams, for all his bravery in making it through two years of solid rehabilitation, has not looked the same player since he first damaged his Achilles in 2009.
Top-flight football has taken chunks out of Williams. Hours in the weights room have added bulk to a frame that would otherwise have been best described as a one-iron with ears.
Much like his predecessor, Norm Maxwell, Williams throughout his career has been happy to be the crash-test dummy and here he is now, still relatively young for a tight forward, seemingly robbed of the elasticity and fast-twitch fibres that allowed him to excel in the test arena.
Hansen has his faith but it is increasingly difficult not to see it as misplaced. Might it not be better, kinder even, to leave Williams at home regardless of what happens tonight and begin the hunt now for a fourth lock for the national team?
Last year Williams had a few moments. This year there have been less. To many that's a pattern - one not likely to change in 2013. That makes Williams a dud investment, whereas someone like Jarrad Hoeata at least has an obvious and considerably bigger upside.
Even Craig Clarke might be worth a punt.
If the remit becomes just about doing a job in November - having a big unit that can handle himself and fit in quickly and easily, then Jason Eaton has wound back the clock in 2012 and done a fair impersonation of his former self.
The luxury for Hansen, if it can be called such a thing, is that Anthony Boric has had career-saving surgery and could, by the middle of next year, be stomping about to the same good effect he managed at the end of 2010.
But who knows, Hansen may yet be sticking another feather in his cap.
He was right to persuade Anton Oliver against retiring in 2004; he was right about shifting Kieran Read from blindside to No 8 in 2009; he was right to recall Liam Messam this year.
It is a stretch to believe he will be right about Williams.
Even the true believers will have their doubts.
