When you have a long, strong suit that is not completely solid, do not immediately assume it must be trumps. Maybe partner has some length that makes a different suit a better choice.
In this deal, North immediately imagines that six or seven hearts will be right, depending on whether partner has the club ace or not. And some players would open four no-trump to find that out immediately. Here, North would end in seven hearts. But what opening lead defeats that contract?
A more circumspect North opens two clubs and rebids two hearts over South's two-diamond negative reply. Then, when South rebids two spades, which guarantees at least a five-card suit and some values, North sees that spades look better than hearts. He launches into Blackwood before bidding seven spades.
West leads the club king against the spade grand slam. South wins with his ace and, believing that there are no problems, plays a spade to dummy's queen. When East discards a club (not a diamond!), South has to rethink. How should he continue?
South must get back to his hand to finesse West out of the spade jack. Declarer cashes dummy's heart ace, ruffs a heart in his hand, leads a spade to dummy's 10, draws West's last two trumps, and claims.
Note that a club lead defeats seven hearts, removing the key entry to the South hand. Yes, that would be unlucky, but remember also that a 4-1 heart break, which would defeat that grand slam but might not stop seven spades, has a 28 percent probability.