Greetings.When I look within myself, that is to say introspect, I see only ideas and notions, some of which are distinct and self-evident and so have the necessary substance of truth, while others appear fleeting and conditional. And in the former category I must admit to identifying a subsection: things that also have the appearance of certainty. In this mode I can easily conceive of a Being who is the cause of all things and whose non-existence is as impossible as the idea of a rectangle with fewer than four right angles. But when I explore this notion further and pronounce that 'There is no Being', I can find no error in the statement. This is because the non-existence of the Being is as clear to me as the idea of its existence. I see nothing that corrects or denies these perceptions, therefore I see nothing within me that proves what it is I'm supposed to see.
There are many ways and aspects to 'look within' and 'know thyself.' In one sense, the development of understanding of what is meant by 'looking within' is part of the process of 'looking within. Looking inward to see ideas, notions, and what can be conceived is one approach but there are other approaches that do not involve these, or thinking at all, or even what may be considered the mind as opposed to pure consciousness. For examples, teachers point towards meditation with stillness of the mind, and to attention focus on pure awareness and consciousness, elements that every human have. Looking within can involve development/change within such as the cases of study and knowledge coupled with contemplation (perhaps related to Zackcool's ponder and reflection?), and of the path of good works coupled with love. In these latter cases, looking within can involve purification. There is much more, too.
Regards,
a..1