One verse

Bhagavad Gita 4.17

4.17

कर्मणो ह्यपि बोद्धव्यं बोद्धव्यं च विकर्मणः | अकर्मणश्च बोद्धव्यं गहना कर्मणो गतिः ||४-१७||

karmaṇo hyapi boddhavyaṃ boddhavyaṃ ca vikarmaṇaḥ . akarmaṇaśca boddhavyaṃ gahanā karmaṇo gatiḥ ||4-17||

karmaṇaḥ
of work
hi
certainly
api
also
boddhavyam
should be understood
boddhavyam
should be understood
ca
also
vikarmaṇaḥ
of forbidden work
akarmaṇaḥ
of inaction
ca
also
boddhavyam
should be understood
gahanā
very difficult
karmaṇaḥ
of work
gatiḥ
entrance

The intricacies of action are very hard to understand. Therefore one should know properly what action is, what forbidden action is and what inaction is.