| Sandbox style also relies heavily on players who are comfortable/interested in taking the initiative. Early on in my DMing career, I once planned an entire encounter on one player's backstory, not realizing that the player in question had absolutely no personal initiative. We spent the entire session plodding along with little to no action or progress, because the player that I'd counted on to drive the action had no interest in doing so.
Know your players. Know whether they're the kind of players who like to drive the action, or the kind of players who'd rather follow a more pre-set path. This will save you a lot of pain.
__________________
signed Jere, Lord of Pendragon
"Raven dark but beautiful, in a malevolent sort of way;
With eyes that speak of wonders on the other side of Day.
She dances in the shadows where others fear to tread;
But though her touch may kill you, it's her love that you should dread." | 
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