“I've been struggling with this. As far as I can make out (back tracking through Heidegger), is that there is no fixed point at the centre of human consciousness (in fact, there is no centre at all) from which we can attempt to discover meaning or truth. We are simply made up of the past and the future, but have no 'core' which transcends this (nothing 'timeless'), therefore trying to seek truth from this standpoint (or non-standpoint) is impossible. Not sure if this covers it, but would be interested in the opinions of others? Thanks.” - Wyrdskein
[On the image above. It's quite possible that Derrida would have taken that as some kind of compliment. But, of course, he would never have said, 'I take that as a compliment'. He would, instead, have said the same thing in pretentious deconstructionese to hide the simplicity and possible banality of his statement.]
I think that the idea of the 'metaphysics of presence' is that there is a strict and determinate one-to-one relation between between a word/concept and our knowledge or cognizance of its meaning. I think Derrida also stretches this to include many - or all - aspects of Western philosophy dating back to the Greeks.
The Western fixation (or belief), so Derrida claimed, is that we could gain a precise and exact grasp of what a word/concept means or, more broadly, what, say, truth, justice and knowledge are. But in the case of words/concepts, that is impossible because words/concepts bear a stronger relation to other words/concepts than they do to their meanings. (Or, in Derrida's jargon, 'signifiers' bear a stronger relation to other signifiers than they do to what they 'signify' – or to the 'signified'.) What you get, then, is a kind of meaning holism in which a word's meaning stretches out, as it were, through all the other words in its language or system or at least to those words to which it is directly connected. That means that no one person, by virtue of that meaning holism, can grasp the meaning - or fully determine the complete meaning - of a word/concept.
This lack of 'presence', or holism, applies also, as I said, to all philosophical concepts such as truth, freedom and knowledge. In other words, there is no 'metaphysics of presence'.
So, yes, there is no fixed center to consciousness either, I suppose; though I'm not sure if Derrida put it that way. However, if this is just a denial of the self, or a critique of essentialism, then Derrida was hardly original in this respect because such a denial is found in Hume and philosophical anti-essentialism dates back to the Greeks.
I also think Derrida’s views on the self and his anti-essentialism are (somewhat) separable from his views on the metaphysics of presence (which I have commented upon); though there are obvious connections.
I'm not sure if I believe all these things. I also find it difficult to understand Derrida. However, I don't think that this has anything to do with the complexity or deepness of his thought. Often what he says, after you have unpacked it, is either pretty obvious or almost truistic. Either that or it has been said before; which is not to say that no other philosopher has repeated what previous philosophers have said. What is different with Derrida, as far as I'm concerned, is, specifically, the ('deconstructive') prose style; which belongs to a particular Continental, specifically French, tradition. Partly because of that you'll find endless neologisms which, to those outside Derrida's fan-base, will be flummoxing. In addition, there is a strong sense of one-upmanship, outflanking, pretentiousness, being deliberately outre, self-conscious philosophical radicalism, philosophical exhibitionism, point-scoring against the (usually French) "radical philosopher" just dead or gone (out of fashion), excess, etc. which also makes his work hard to understand - at least as far as I'm concerned. But if you said all that to Derrida, or a fan, you wouldn't be able to understand the reply in defence. And that would no doubt be the intention.