I think that there are precise reasons why the concept of consciousness is particularly tricky.
One reason is that the common idea of consciousness contains a fundamental ambiguity between two sides of it. On one side, consciousness is popularly agreed as knowledge: if I know that a chair is here, then I am conscious that a chair is here. The problem with this concept is that it is quite mechanical, so that it seems to imply that even a pocket calculator knows that 2+2=4. Despite this ability, we feel that the calculator lacks something. One thing that it seems lacking is freedom: a calculator is not able to freely decide a moment when to think about 2+2=4. The problem is that even about ourselves when cannot get objective evidence that such freedom exists in us.
Another reason is the confusion between repeatability and uniqueness. I feel my experience of consciousness as something unique and exclusive that is happening in me here and now. But, at the same time, the concept of consciousness exists and is understood, to a certain degree, because we treat it as something not unique, but shared by many humans, may be even by animals and, why not, plants and objects. Consciousness as a non unique concept is, after all, the consciousness of the pocket calculator: we treat it as just a phenomenon, an object. This conflicts with the exclusive uniqueness that I feel in myself when I pay attention to my ongoing experience of my present consciousness.
There is another fundamental confusion in the nature of language. Language can express shared things only. If something is entirely unique and exclusive, the consequence is that there is not a word for it. This means that the word “consciousness” is able to refer to those aspects of consciousness that are shared only. Ultimately, this is again the consciousness of the pocket calculator. But I feel in myself an ongoing experience that I can only feel, not tell, not tell to others, not even tell to myself. This is a very bizarre experience, because I feel that it is definitely in me, always available to myself whenever I decide to think about it, but, despite this seemingly such a strong and undeniable evidence to me, I must acknowledge that it is strong to me exclusively, strong as a feeling, but absolutely impossible to express by words even to myself.
I think that the basic ambiguity that creates all other ambiguities is the way how we conceive subjectivity. There is an objectified concept of it: it is when I think about your subjectivity, other people’s subjectivity or the abstract concept of subjectivity. But there is also an experience of subjectivity that it is impossible to objectify. It is to me my experience of my subjectivity. It is impossible to objectify it because it is impossible to express it.
Now you might wonder what I am talking about, since I have said that there is at least one side of consciousness and of subjectivity that cannot be expressed. There are two reasons why I have tried to talk about it all the same. One is that probably you experience like me something that we could call consciousness, or self, or subjectivity, that you, like me, feel impossible to express as well. This is just a free hypothesis of mine. In this case you might be able to find in yourself what I am referring to, but it impossible to me to express. The other reason is that, in my opinion, the two aspects of consciousness and subjectivity, that is the objectified one and the inexpressible one, the pocket calculator that is part of my brain and my unique exclusive feeling, are connected to each other and in a continuous dialogue with each other. This means that whenever we talk about one side, the other side is actually always present as well behind our words.