The basic problem is not the lack of understanding what is being told by the ancient sages. The problem is the fact that one often approaches the knowledge as an individual. As long as there is an idea or the thought that one is an individual (the dictionary meaning of 'individual' is 'a distinct indivisible entity'-how ironical!), one cannot "get it". Can there really be two selves? Obviously not! There is only one Self and that is unquestionable. In that case, who is this other self who wants to know about the Self? ( In this case Self means the pure I AM, or the Absolute Consciousness or Brahman/ Atman). Therefore, unless and until one establishes the identity of this other self, there is no way the understanding will be complete. So, let us look at who exactly is this individual, the small self, the seeker who wants to know.
One has to track backwards to where the idea of individuality first arose. As an infant there is no idea of individuality. Everything is just as it is, without idea of separation of 'I' and 'not-I'. The infant does not see himself/herself as a separate entity in this world around him/her. It is therefore not uncommon for little children to speak in third person. For instance, a kid may say "Jimmy want water", or "Jimmy hungry", meaning he wants water or that he is hungry. He does not as yet say, "I want water" or "I am hungry". He thinks that since everyone calls the body as Jimmy, he also assumes the body (his body) is Jimmy- a third person. Subsequently, somewhere between 18 months and 3 years of age, repeated reinforcement and conditioning of the mind takes place and establishes the idea that 'I' means this body. The mother may repeatedly enforce the idea that she is the Mommy and he is Jimmy. Slowly, the idea of 'I am the body" and whatever is not this body is "not-I" gets established. This is where the idea of separation starts. Separation of this 'I' from the rest of the world. A creation of a false subject called 'I', the first person, is established. He gets the idea of 'mine' and 'not-mine' or 'theirs' etc. This separation of what is essentially One into multiples is the beginning of suffering. There is thereafter a constant sense of incompleteness and a longing for completeness. This longing for completeness is called suffering. This separation results in a feeling of insecurity and vulnerability. A feeling that someone out there will eventually take away what one has. This results in one closing the open doors to the world out there. The open-ness is no longer there. One becomes more and more encased in an artificially created shell to protect this identity of individuality. The innocence that is associated with early childhood is slowly lost as the sense of being separate is reinforced more and more as the years go by. This results in suffering as there is feeling of incompleteness. The seeking (for fullness and completeness, essentially translated as peace) begins at this early stage of life. A seeking for completeness. A seeking for peace and happiness. A seeking for something, any thing which many don't know what but still look for. Unfortunately, the seeking may result in looking for a thing, an object and this may cause more suffering as it may bring only transient happiness. This seeking may manifest itself as hoarding of objects (called materialism) or plunging oneself into other ventures like religion, spirituality (called spiritualism), drugs, alcohol, relationships, or anything else, that will for a short period of time take away the thought of individuality, thus resulting in transient peace. This peace is what one is constantly seeking. However, one wants permanent peace in the world of transient objects!! Is that really possible?! This seeking for an end to suffering is the reason you are reading this material. What you are really seeking(although unknowingly) is an end to the very idea of individuality.
When one feels happy, it is the absence of individuality, meaning thereby one forgets oneself. In that momentary forgetfulness, there is a feeling of fullness and contentment. The end of separation, however transient as it may be, is what one is looking for. Although, one may not know it! It becomes clear that one can be at peace only when one loses oneself! In fact, this is experienced by all every single day. In deep sleep, there is no idea of 'I am the body' or 'I am the mind', or ' I am a man' or 'I am so and so' . Yet, there is undeniable peace experienced by all in deep sleep. Even though the individual is absent in deep dreamless sleep, one cannot deny that they exist. Who is this one that exists in deep dreamless sleep? Obviously, there is no Jimmy in deep dreamless sleep. The One who exists in deep dreamless sleep is the Real YOU! Yet, you say, I do not know who this One is. This is because, you expect this One to be an object like all other objects. Can the Subject be the object? If so, how can it be called the Subject? Can you please describe objectively your experience in deep dreamless sleep? Obviously, not! What you can say with conviction and certainty is the experience of peace in deep dreamless sleep. Is that not why we look forward to sleeping? Even though we know very well that we will kill the very idea of individuality that we so carefully preserve during the waking hours? If we really cared about the individual, would we ever sleep, knowing that the individual will be lost in deep sleep? Innately, we all want to lose the individuality, since we innately know the peace that comes with losing the sense of individuality, the sense of a separate "I".
Thus by inquiry into this individual, this "I-thought", one can come to know the falseness of this individual. By knowing what you are not, you know who you really,really ARE. For you already are THAT. Just remove this sense of being a separate individual. Knowing that there is no-one (meaning no individual) here to have knowledge or ignorance is the key to the final Understanding of the sayings of the ancient sages and rishis.