At the end of Episode 3, Obi-Wan (soon to be known as Ben) Kenobi hands over the baby Luke to his closest living paternal relatives - Owen and Beru. The next time Kenobi and Skywalker meet again, it's almost 18 years later.
Why 18 years, I wonder? Why didn't Ben make a move earlier on?
Why, Uncle Owen, I imagine. We first meet him in Episode 2, and it's clear that Owen grew up to become his father, Cliegg - not a very complicated man, who believed in hard-work, generosity, dignity, protecting one's family - and not in 'damn fool idealistic crusades'.
Were Obi-Wan and Yoda aware of this when they handed baby Luke to the Lars? Probably not. They most likely assumed that the Lars adored the Jedi like the rest of the Republic. So what happened when Obi-Wan mentioned training the boy to Owen?
"You come any where near my boy with that lightsabre of yours, and there'll be Hell to pay! You ruined Anakin's life with your damn Jedi ways, don't you dare ruin Luke's!"
It must have been extremely frustrating for (rapidly becoming) old Ben. This was his life's work - training the 'New Hope' until he's strong enough to murder his father. But he's not allowed to do so. Thanks to a half-educated farmer and his cynical philosophies.
Then to make matters worse, when he does get precious one-on-one time with Luke and he gives him his sales pitch, what does the 'New Hope' say? "I have too many responsibilities on the farm."
Remember Ben's ominous words: "That's your uncle talking."
Over the course of Luke's lifetime, Owen Lars had gone from a convenient baby-sitter to a big liability and clog in the wheel of the Jedi's idea of destiny.
So when the stormtroopers rode into the farmstead that hot Tatooine day to re-claim the fugitive droids - could Ben have done something about it? He had had enough dealings as one of the foremost citizens of the Republic to understand how the system worked. If a droid had top-level intelligence information, was it unlikely that top-level intelligence operatives would be close on that droid's heels? Let's assume for the sake of argument that he knew this.
Did he sit back and hold his peace? After murmuring those words, "You must do what you must, of course," did he deliberately stay silent, let events unfold naturally without raising a finger to stop them? As the stormtroopers burnt down the homestead and the closest thing Luke had to family, was Ben Kenobi calmly walking beside Luke, feigning surprise and slow realization as they came upon the Jawa's sandcrawler?
Were Owen and Beru sacrifices to the Will of the Force as the Jedi perceived it?