aasureem yonimaapannaa moodhaa janmani janmani |
maamapraapyaiva kaunteya tato yaantyadhamaam gatim || 20 ||

Entering into devilish wombs, the deluded individuals, from birth after birth, do not attain me, O Kaunteya. They attain destinations even lower than that (state).
aasureem : devilish
yonim : wombs
aapannaahaa : entering
moodhaa : deluded individuals
janmani : birth
janmani : birth
maam : me
apraapyaiva : do not attain
kaunteya : O Kaunteya
tataha : than that
yaanti : go
adhamaam : even lower
gatim : destinations
Here, Shri Krishna expresses his regret about a lost opportunity. Anyone who has attained a human birth has a chance to achieve self realization and liberation. But those individuals who engage in destruction of others instead of improving their state give up this golden opportunity. Such people enter a never ending descent into lower and lower realms of existence. An example given in most commentaries is that of kumbhipaaka, where individuals spend their time in a pot of boiling oil.
Such is the rare and special nature of a human birth, that most spiritual masters have mentioned it in their texts. Shankaraachaarya begins the Vivekachoodamani text with this proclamation : “For beings a human birth is hard to win, then manhood and holiness, then excellence in the path of wise law; hardest of all to win is wisdom. Discernment between Self and not-Self, true judgment, nearness to the Self of the Eternal and Freedom are not gained without a myriad of right acts in a hundred births”.
The practical implication of this shloka is the importance of free will. Only a human has the ability to shape his or her destiny. Plants, animals and birds cannot do so. All they can do is follow their instincts and their sense organs. If we also start ignoring our intellect and empowering our sense organs, there remains no difference between us and animals. We lose all traces of sattva, and only exist through rajas and tamas.