On this particular hand, North rates to have 3 spades, 5 hearts, and no minor-suit shortness to go along with minimum game-forcing values. If North's hand is xxx KJxxx Kx KQx, then you can safely exit a heart every time you're on lead, likely taking one or two hearts, two spades, and a diamond (Note that this is a hand that stretched to make game, and even this dummy may allow declarer to make, e.g. when holding AQTxxx -void- QJxx Axx).
If, on the other hand, dummy shows up with Qxx AKQJx Qx xxx, you're in trouble. Your opening heart lead may have given declarer a chance to pitch two quick minor-suit losers, and you're only taking one trump trick.
So a reason not to double with this hand is this: On the auction, partner probably has two important cards. It would be surprising for partner to have two aces, and if one of their cards is the diamond king or queen, it's probably being picked up.
Let's look at the odds for doubling in various situations. This table gives scoring form on the left (total points and international matchpoints), and vulnerability on the top. In each box is W/L/P, where W is the score gained when doubling and defeating the contract with one undertrick (vs not doubling), L is the score lost when letting 4Sx make with no overtricks (vs 4S undoubled making), and P is the probability that you defeat the contract by one to make doubling a worthwhile action.
| | NV | V |
| TP | +50/-170/77% | +100/-170/63% |
|IMPS| +2/-5/71% | +3/-5/63% |
At matchpoints, of course, if everyone is in 4S, you need a 50% chance of setting or better to make doubling worthwhile.
Of course this is a simplification; it doesn't take into account the chance of taking two undertricks or the opponents making with an overtrick. On this hand, I haven't done any simulations but I would say that you certainly won't defeat opponents on three deals out of four, and probably not on two deals out of three, but may one deal out of two; I would consider doubling when playing matchpoints but not at other forms of scoring.