It became a thing due to the experience of self-reflection. The million dollar question is how come humans (and few other organisms) are able to self reflect on their biology, life situations, logic, math and even consciousness itself? However complex and sophisticated a machine's brain is, be it biological or mechanical (AI/AGI), no known laws of science allows it to self-reflect. This is famously called "the hard problem of consciousness" in philosophy which remains unresolved to this day.