So it might just be with Sonny Bill Williams, an 18-year-old tank not long out of Mt Albert Grammar, who exploded on the NRL stage with a 1000-megawatt debut for the Bulldogs against the Parramatta Eels.
Williams - he sounds country and western but the effect is pure heavy metal - went into the game with, as they say, big raps on him.
Laurie Daley, who knows a fair bit about league stardom, reckoned before the game the 1.91m, 102kg steamroller would go on to be one of the greats.
After Williams set up one try with a surging 60m run, had a hand in another try and scored one of his own, Daley chimed in with "they only come around once every 10 to 15 years and he's one of them''.
Nathan Brown, coach of the St George Dragons, who had felt the big teenager's force in a pre-season game, weighed in with the weighty: "He's the best 18-year-old I've ever seen - and I played with Gorden [Tallis].
"He's going to be a star. If you put every back rower on the market now he'd be the one I'd take.''
But if Williams appeared overawed by the talk before he'd run on to the field, it didn't show. Mind you, it helped that the Bulldogs were playing an Eels side who looked as comfortable as a kitten at a dog fight.
Now Williams is raw and might not live up to the hype. Australians are big at dishing it out, if not always to New Zealanders.
But on first sighting, which is often not the most accurate guide, Daley might just be on the money.
