There are many things in life that can only be really understood after we have become parents who have offspring.

There are several reasons why prehuman civilization is kept secret by ruler of this world. One of them is to avoid warfare between those who can and those who can't accept that humans are descendants of something else.

There are people who believe in the existence of angels, but do not believe in alien existence. There are people who believe that aliens and angels are the same creatures. But there are people who are much worse, those who have seen and met angels, and witnessed the presence of aliens, but does not admit even the slightest about the linkage between both. And the worst thing is, they even try to maintain the status quo.

You do not say 'It's classified' to a certain thing needs to be hidden, because people are going to find it in anyway possible. Say it in a way with your language that gives people a benefit of the doubt.

The common reason why human mind is so difficult to accept and believe in the alien existence, actually has something to do with the possibility of the existence of some unknown creatures, which may far more advanced than human in terms of knowledge and know-how, yet at the same time people assume that human is in the top level of food chain pyramid on this planet earth.

If I lie about truth which you will know somehow later,
then you would call me a liar. But If you're willing to dig
further about truth that force me do it, then you would
understand my reason. But you wouldn't acknowledge it.