The ten is right for technical reasons as well, if RHO wins the heart and plays a club back our main chance is going to be taking 3 spades, 3 hearts, 2 clubs, and 2 diamonds. We are going to need the jack of hearts to be doubleton, and if it is the 9 of hearts being an entry will be crucial to our plan as we are an entry short to both finesse spades and cash the king without it. Also if LHO has something like AJxxx of hearts and works out to pop ace we will be much better off having unblocked the heart ten. The only alternative to playing the ten of hearts seems to be playing the queen of hearts. Since they must win, we guarantee 2 entries to dummy. If we could somehow combine chances in hearts and spades this might be a serious option, but we can't. After someone wins and plays a club, we win it and go to the diamond king and hook a spade and cash the ace of spades. Now we will have to guess whether or not to hook the heart (going for 3 spades, 3 hearts, 2 clubs, and 2 diamonds), or play a heart to the king and hoping spades split if the jack doesn't fall (going for 5 spades, 1 heart, 2 clubs, and 2 diamonds). Compare this to having led the HT at trick 2 and LHO wins the ace, in that case we are going to make if either hearts or spades come in in that situation. Of course, compared to RHO having won the ace we are much better off starting with the queen than the ten, but that just means if the opponents are going to win the ace, half of the time we are much better off starting with the ten, and half of the time we are much worse off starting with the ten. Given that, I would like to keep the main upside of LHO forgetting to win the ace of hearts, nobody is perfect.