When you have lots of the opponents' trump suit, that best defense is what is called the “forcing game.” You lead fourth best from your longest and strongest, hoping partner has a little help, and you can end up “forcing” Declarer to ruff in the long trump hand. After Declarer has to ruff once or twice in the long trump hand, s/he will often lose control of the hand—you end up with more trumps than Declarer.
Hand today went 1♠ on your right. You held: ♠J8764 ♥K10643 ♦A10 ♣4.
You pass. LHO bids 1NT (forcing) and RHO rebids 2♠ ending the auction. Your singleton club is tempting, but the best percentage lead is a fourth best heart—looking for the tap (forcing) suit.
If you lead a heart, dummy shows up with:
♠9 ♥A72 ♦963 ♣KQJ872 and Declarer takes the ♥A while partner signals encouragement (standard signals) with the ♥8. Declarer plays two top spades and partner plays the ♦2 on the second round. Declarer's best shot is to abandon trumps at that point and force out the ♣A. Partner will probably take the first club as she cannot tell from the spots whether you have one club or three. She will return the ♥Q and Declarer will ruff. (Now both you and Declarer have 3 trumps each.) The best Declarer can do is play a club to dummy. You can ruff that and return a third heart. If she ruffs and plays a third club, you ruff and return the ♥K. She can discard one diamond, but you still have a fifth heart to play. She must ruff that and can pull your last trump, but then has to play diamonds from her own hand. In that case, Declarer gets six spade tricks and the ♥A, but makes NO minor suit tricks.
If you lead your singleton club, partner will take ♣A and return the ♣6 (higher of two remaining) for you to ruff. If you trump and return the ♥K (also to kill Dummy's entries), Declarer can take the ♥A and take 3 top spades; then give you a spade. If you don't take your ♦A, everything goes away on the club in dummy and Declarer will take 10 tricks.
Ironically, if you do NOT ruff the initial club return by partner (waiting to ruff the third round when Declarer plays her last club), Declarer has more of a problem. Double dummy, her best shot at that point is to run the ♠9, letting you win your jack (playing you for long trumps). Now the heart shift is too late. She can ruff a heart to her hand, pull your trumps and still get back to dummy for discards, still making 10 tricks. If she tries a diamond to the Jack instead of the ♠9, she'll develop a diamond trick and still end up making nine tricks. Your side will get two spades; one diamond; one club.
Bottom Line: Declarer will almost always fail with a heart lead and almost always make (often with overtricks) on a singleton club lead.