Safety plays in bridge are simply sacrosanct for all those who take their bridge seriously and wish to be in the run for the front rankers of bridge. When we talk of safety plays we are in fact talking of paying insurance for the safety of our contract from all those wild distribution that can jeopardise an otherwise normal contract.
Safety plays come in various ways and the expert recognises their need earlier than all the other average and above average bridge players. Some are of course now recognised as standard safety plays that should be on the fingertips of every serious bridge player with the intricacies of suit breaks and their effect on the overall outcome of the contract. Of course when you change your priorities and put safety play on top, it means that you recognise the need to shift gears from the normal routine line of play. To take a simple example say one holds touching honours such as KQ or J10 or QJ and wish to force out the opposing winners, the natural inclination prevalent in all bridge players would be to attack with the play of one of the touching honours.
But first things come first. The contract is the key and the making of it the final goal, so to ensure its fulfilment, bridge players need to have insurance, that is the safety play to guarantee that no wild distribution of cards can defeat it ever. In the above context, you need to abandon the normal line or acquire some finer technique to achieve your goal. Lets find out with our first illustration placing you in the south seat.
In a contract of 4H, you receive the opening lead of the QD. What are your prospects overall? First things first. You know you have a spade loser and need to restrict your trump losers to only 2 and not 3. Taking the first trick with AD, you cash the AH in dummy and come to hand with AC. The vital question is what next? For you have reached a critical point of declarer play on which depends the fate of your contract. In other words, the handling of the trump suit is very crucial when you need to play your cards in a manner that would restrict your trump losers to 2 and not any more.
It is here that the need and benefit of safety play should takes precedence over everything else. The average player would remain in the illusion that if he plays anything else but the J or 10 of hearts, the opponents might win a cheap trump trick without using an honour.
It is this illusion, which demarcates the average from the expert. For the latter can see through that if the hearts are 3-3 south would always be able to clash the opposing honour in the third round giving the opponents just 2 tricks. In that case, it is an illusion to think that a low heart lead would make a difference for that would make no difference in the outcome of the contract. Of course in the extreme case where one of the defender holds KQ9X, the defenders shall always defeat the contract by taking 3 tricks anyway. So the safety play rule No I clearly points out that it can never benefit the declarer to lead J or 10 on the second round for in this particular illustration the trumps were distributed as under with west holding Q9 and east K876 - a 4-2 break that has a far greater percentage than a 3-3 break.
Now do you see if you had played J or 10H on the second round, west would crush your honour with the queen and thereby promote his partners K8 as potential winners. Let me conclude the safety principle with a trump combination of 7 opposite KQ8532. In order to guarantee no more than 2 trump tricks for the defence, declarer would never gain if he started with K or Q on the first round for say if one defender holds AJ10 under your long spades, he will score two tricks whether you play the K or low. But if west holds singleton A and east J1096, playing from a honour would be violating safety play rule and giving opponents 3 trump tricks. So it is better to play safe and smile.

==================
North        South
KQJ            987
A          J105432
AK654            3
K632           AQ7
==================