Imagine you just had the worst day of your life.
Well, it wasn’t really a day. Hours and days have no meaning for you. You have lived far too long to follow such microscopic temporal distinctions. You built an empire, and lived to see it dying. What can a day matter? A year?
How about a thousand?

Your planet was dying. Your species was dying. What can a king do, when his children are dying because there is nothing to eat? You knew the answer: The Allspark. You hung onto that fairy tale even as your followers declared it absurd, taking off immediately, all alone, as soon as there was a sign of it. No delays; Without the Allspark, everything you ever knew and loved would slowly wither away and die. And all you needed to do was move to a completely insignificant planet it found itself drawn to and pick it up. You would be more than a leader, you would be a hero, a saviour. There would be no more need for war, no more fear of death and hunger, and no more dying younglings.

And then everything went wrong.

The moment still constantly plays before your eyes. You break into the planet’s atmosphere, and it nearly destroys your sensors. That vivid feeling of total disorientation, the hard, sudden impact, and the cold darkness that closed around you as the cavern froze around your unmoving body. You weren’t ready to die. You thought back to your planet, your people – you still had to save them. Had to. What would they do without you? The people saw their leader off, promising them to bring back utopia. Knowing you wouldn’t return would shatter their morale completely.

The years start piling on. You try to move, try to melt the ice, try to do anything, but the world only seems to become colder around you. Ten years. Fifty years. Five hundred years. Unable to move, with only your own thoughts and worries to give you company. Your mind can’t take it, and your sanity falls apart. Everything you thought and wished for slowly shatters into pieces, leaving only hate and chaos behind. Eight hundred years. Thousand years. After a while, you simply stop counting.

Then you hear a crash from the ceiling.

Through your delusional fever dreams, you aren’t sure if it is real or not, or what is truly happening. A tiny creature descends upon you, clearly primitive, shouting in rough, poorly-coordinated language, but perhaps not too dissimilar to you. You failed to bring the cube to your people – but maybe, maybe there is some slight chance that he can. So you tell him where he can find it, the only way you can right now. You rest a bit more easy. Perhaps it is time to rest after all.
But, more small creatures start filling your cavern. They begin chopping away at the ice that binds you, clumsily, but surely. They want to free you. For the first time in millennia, you feel just that little bit more warm - finally you will be able to return, to not be a useless statue, but the great hero you were destined to be. Your silent cheer fills your own head as the humans, as they call themselves, with great difficulty, raise you out of the cavern and put you onto a transport.

They seem bewildered with you. Curious. A little too curious, perhaps. As grateful as you are, you have a mission to attend to, and they will only get in the way. You are defrosted enough to stand up.

Panicked shouting erupts among the small ones. It seems they hadn’t expected you to still be alive. You notice too late the all-too-familiar cold creeping up your body, and suddenly you cannot move again. They froze you!
Burning rage fills your heart. What do they think they’re doing!? They lock you underground again, and, to your horror, begin to force parts of your body open, dissecting you alive.
You start picking up on their language, and slowly begin to understand what they’re saying. They’re just using you to expand their technology. These primitive insects have attached themselves to you like filthy parasites, using your suffering to create for themselves more meaningless conveniences. You should be their god. You wanted to save your own kind, but instead, you are treated like a chunk of garbage. And as a final injustice, the insult to the injury, they did not even treat you to a proper name.

Needless to say, as soon as you are free, someone will pay.
—-
Well this was a bit fanfiction-y, but I really can’t underestimate what a massive bum deal Megatron got before the movie even started, because it’s going to be a pretty big deal from now on. It’s really interesting how the movie doesn’t really show or tell you any of this stuff, but just lets a few loose ends hang (Megatron’s understanding of the language, his imprinting on the glasses, his change in location, the reverse-engineering, peeps keeping him artificially frozen) and relies on you to follow them backwards until they come together to form a coherent narrative to understand the antagonist’s actual motivation. That’s a pretty bizarre thing of a movie to demand when it ostensibly wants you to watch with your brain turned off, is it not?