"Tell me what you regard as your greatest strength, so I will know how best to undermine you; tell me of your greatest fear, so I will know which I must force you to face; tell me what you cherish most, so I will know what to take from you; and tell me what you crave, so that I might deny you." - Darth Plagueis

Killing Han Solo was not enough.

Killing his father was not enough.

You can feel that he hates himself for it, regrets it.

You underestimated the depth of his loneliness and depression.

You thought - wrongly - that slaying Solo would free him of all sentimentality.

I've never felt so alone.

You're not alone.

Neither are you.

The exchange delights you because it could not be more pure. The quiver in his voice as he speaks to her, trepidation when he tells her she is not alone. The way his emotions swell when she answers in kind. You were quick to note the spark of compassion he showed the girl, a spark that could be exploited.

Exploit his absolute desperation to be accepted by someone. Anyone.

And she is so lonely.

You feel it. He cherishes her, craves her.

He's falling in love with her.

You know it to be true because he hides the connection from you, from the Supreme Leader. Keeping her all to himself.

Let him hope for a moment that it is possible for someone to love him.

For her to love him.

All while not knowing you were the one to fabricate the connection.

It is cruel, and it is perfect.

When the time comes he will drive a saber through her chest and thus his own heart.

His heart, though he does not know, is his protege's greatest weakness.

He will learn firsthand that love can die, that he will be more powerful without her.

Finally, his training will be complete.

I know Leia and Han love their son, but I always thought Ben's depression + his interpretation of their rejection (sending him to Luke's Jedi camp) + Snoke's abuse warped him into thinking no one did. Until Rey came along.