Concentration and Meditation
A strong and regular practise of Asana and Pranayama is important as a preparation for holding the meditation postures longer, but it's not a precondition.
Meditating is to look at the surface of the mind and to slowly dive into its mystery.
During our life we experience bliss, disappointment and much more.
Yoga philosophy talks about Viveka (discrimination, distinction) and Vairagya (dispassion, detachment).
And we start to learn, how we can "distinguish" between things, events and incidents.
For me, this is the most important lesson in Yoga. To understand it completely, more than one incarnation is necessary?
(Just stay on the ball :-)
"The distinction between real and unreal, personal experience and spiritual bliss and to finally merge into the consciousness, that the inner self in you also is the self of everything - this is liberation."
(Vivekach?damani, Sri Sankaracharya)