“The sages answered with a story still told after thousands of years. Imagine, they said, a man dreaming that he is being attacked by a tiger. His pulse will race, his fists will clench, his forehead will be wet with the dew of fear – all just as if the attack were real. He will be able to describe the look of his tiger, the way he smelled, the sound of his roar. For him the tiger is real, and in a sense he is not wrong: the evidence he has is not qualitatively different from the kind of evidence we trust when we are awake. People have even died from the physiological effects of a potent dream. Only when we wake up can we realize that our dream-sensations, though real to our nervous system, are a lower level of reality than the waking state.
The sages called the dream of waking life – the dream of separate, merely physical existence – by a suggestive name, maya.
Easwaran Ed., Eknath. The Bhagavad Gita”
Think of it this way, there is one eternal truth or universe or energy-space or Brahaman. The day to day reality we see and believe in is manifestation of this Brahaman through the filters of our mind. Just like when you see with naked eye, you see a metal table, but if you look close enough with an electron microscope, you see atoms and molecules, with vast spaces between them. What appears whole and tangible, is not whole and tangible, it is a collection of discontinuous specs of matter, which in themselves are just energy trapped in form of matter.
So in a sense, we are all in a dream state of this life. What we consider real, for example, our body, our ego, our prestige, our honor, are all artificial constructs borne out of the very nature of this illusion. This illusion is Maya.
We love Maya, we are attached to it, we think it is all there is and we do everything to get totally immersed in it and live our fleeting lives in its consumption.
As per Geeta, one who can be immersed in Maya, yet knows the reality, one who does his/her karma, playing the role one has in this Mayajal, yet remains detached from Maya, she/he is the one who truly lives a good life.