Hi there
If the government wanted to hide the flat earth, why does this forum exist? Why do 1000000 youtube videos about flat earth exist? It would be so easy to delete them all.
Explain me.
If they don't see us as a threat I imagine. Their wide reaching arms are far better served making an example of us by creating an environment that shuns flat earthers and others that have 'wacky' ideas.
I assume this quote was floating around in your head without the proper context. I'll help you out, no problem 
First of all, the proper quote is
"For the first time he perceived that if you want to keep a secret you must also hide it from yourself"
Context:
In Orwell's 1984 dieing as a martyr is rebellion
"The first thing for you to understand is that in this place there are no martyrdoms. [...]Inquisition. It was a failure. [...]For every heretic it burned at the stake, thousands of others rose up."
"Even in the instant of death we cannot permit any deviation."
Dieing while you hate the party/big brother is rebellion
"They would have blown his brain to pieces before they could reclaim it. The heretical thought would be unpunished, unrepented, out of their reach for ever. They would have blown a hole in their own perfection. To die hating them, that was freedom"
The Party seeks to remove every small piece of freedom from oceanias citizens to manifest its power.
"The Party power entirely for its own sake. [...] Not wealth or luxury or long life or happiness: only power, pure power."
Therefore, Winston decided that his final act of rebellion against the party would be to sabotage their plan
"We convert him, we capture his inner mind, we reshape him.[...] We bring him over to our side, not in appearnce, but genuinely, heart and soul."
So Winston plans to "die hating them"
To fullfill his last plan, to be able to perform his final act of rebellion, he would have to hide the secret from himself. If he would not do so, his plan could not succeed since
"mere control of the features was not enough"
As O'Brien could detect any emotion, nearly every thought and thus would not kill him as long as he had a last bit of resistance inside of him; making it impossible for Winston to accomplish his plan, he has to hide his plan from himself.
I do not think any further explanation is needed with the given context. If you still do not understand why and how you used your "quote" wrong, you might reread the book.
Orwell clearly knew the truth. I particularly like this excerpt which seems very pertinent to my last point:
‘Unimportant. We shall conquer them when it suits us. And if we did not, what difference would it make? We can shut them out of existence. Oceania is the world.’
‘But the world itself is only a speck of dust. And man is tiny — helpless! How long has he been in existence? For millions of years the earth was uninhabited.’
‘Nonsense. The earth is as old as we are, no older. How could it be older? Nothing exists except through human consciousness.’
‘But the rocks are full of the bones of extinct animals — mammoths and mastodons and enormous reptiles which lived here long before man was ever heard of.’
‘Have you ever seen those bones, Winston? Of course not. Nineteenth-century biologists invented them. Before man there was nothing. After man, if he could come to an end, there would be nothing. Outside man there is nothing.’
‘But the whole universe is outside us. Look at the stars! Some of them are a million light-years away. They are out of our reach for ever.’
‘What are the stars?’ said O’Brien indifferently. ‘They are bits of fire a few kilometres away. We could reach them if we wanted to. Or we could blot them out. The earth is the centre of the universe. The sun and the stars go round it.’
Winston made another convulsive movement. This time he did not say anything. O’Brien continued as though answering a spoken objection:
‘For certain purposes, of course, that is not true. When we navigate the ocean, or when we predict an eclipse, we often find it convenient to assume that the earth goes round the sun and that the stars are millions upon millions of kilometres away. But what of it? Do you suppose it is beyond us to produce a dual system of astronomy? The stars can be near or distant, according as we need them. Do you suppose our mathematicians are unequal to that?
Have you forgotten doublethink?’
Winston shrank back upon the bed. Whatever he said, the swift answer crushed him like a bludgeon. And yet he knew, he KNEW, that he was in the right. The belief that nothing exists outside your own mind — surely there must be some way of demonstrating that it was false? Had it not been exposed long ago as a fallacy? There was even a name for it, which he had forgotten. A faint smile twitched the corners of O’Brien’s mouth as he looked down at him.
‘I told you, Winston,’ he said, ‘that metaphysics is not your strong point. The word you are trying to think of is solipsism. But you are mistaken. This is not solipsism. Collective solipsism, if you like. But that is a different thing: in fact, the opposite thing. All this is a digression,’ he added in a different tone. ‘The real power, the power we have to fight for night and day, is not power over things, but over men.’ He paused, and for a moment assumed again his air of a schoolmaster questioning a promising pupil:
'How does one man assert his power over another, Winston?’
Winston thought. ‘By making him suffer,’ he said.
‘Exactly. By making him suffer. Obedience is not enough. Unless he is suffering, how can you be sure that he is obeying your will and not his own? Power is in inflicting pain and humiliation. Power is in tearing human minds to pieces and putting them together again in new shapes of your own choosing. Do you begin to see, then, what kind of world we are creating?