Against 4♥ West leads the ♣10, won by East’s Ace. A Diamond shift is clearly called for, and the standard play from that holding is the 10, the so-called “top of an interior sequence.” Is that your choice or are there other considerations?
If West has Ace doubleton in Diamonds, then East can envisage a trump promotion if West also has the right trump holding. But, as it happens, West has ♦A, Q, and the danger is that West will win the ♦Q on the first round of the suit. That would be the right play if East held a trump honor but not the ♦K, but it would be disastrous on the actual layout, killing the chance of a trump promotion.
In the middle of the hand (starting at trick two), many partnerships play “attitude leads,” whereby shifting to a low card usually shows a high card in the suit and shifting to a high card is either from a weak holding or from the top of a sequence. So, reasoning that it is more important to advertise his ♦K than it is to make an ambiguous interior sequence lead, East shifts to the ♦2. Of course, West must be alert and majestically squander his Ace on that trick. Then, back comes the ♦Q overtaken by East’s King, and the third round of Diamonds promotes the setting trump trick. Nice defense!
What a spectacular deception! Next, imagine that West holds ♦A, Q, 9 and East ♦K, 10, 2. Again the opening lead is a Club to East’s Ace and again a low Diamond comes back. West, who is a shockingly devious fellow, wins with his Ace and returns the ♦Q. East overtakes that and sends back a third Diamond. Naturally, Declarer ruffs high, and later finds out to his chagrin that trumps are 4-1 and that he has just gone down in a cold contract!