One of the great unsolved problems of philosophy is the Hard Problem of Consciousness. It's usually defined as something like the following: "Why do we have subjective experience?", or "Why do qualia exist?", or "Why does red look like THAT?". It's the question of how the physical activity of brain cells can lead to conscious experiences which seem to have properties that can't have anything to do with brain cells. The Hard Problem involves very common questions, as being puzzled about the origins of one's experiences is a widespread human experience. But what actually is the problem? Does it even exist?
What can it mean for such a problem not to exist? It means that what is going on in terms of mind and experience isn't what we think is going on and because of this the questions being asked aren't the right ones. An analogy is wondering why the rain god is allowing crops to wilt - this is begging the question about the supernatural origin of rain. There is a question - why isn't it raining? - but it's a different one.
A possible way to try and understand what the Hard Problem is about is to take a look at why we ask it - what are the reasons for asking the question, for thinking there is a problem. This is where it gets a bit murky. We can have certain beliefs about the nature of our consciousness, such as that various things we experience are being experienced at the same time, but it can be easily show through psychological tests that such beliefs are not always true. Our feelings about our experiences involve memory, and memory is built and rebuilt as time passes - it's not as reliable as we might think. The problem is that we are trying to use a facility we don't understand - our minds - to analyse something we find mysterious - conscious awareness. There are none of the usual tools of scientific investigation available. It may be hard to see how conscious experience is the result of brain cell activity, but without having encountered conscious experience that definitely isn't the result of brain cell activity we have no evidence to support the position that conscious experience can't be the result of brain cell activity. We don't even know if there is a real problem or if it's just a mistake.
We can't use a feeling of mystery to make judgements about the nature of something we don't yet understand, and yet that seems to be the basis for so many statements about the Hard Problem of Consciousness. We have no evidence that the problem even exists.