Bhagavad Gita 4.18 · BG 4.18
Chapter 4Verse 18
Jnana Karma Sanyasa Yoga
कर्मण्यकर्म यः पश्येदकर्मणि च कर्म यः। स बुद्धिमान्मनुष्येषु स युक्तः कृत्स्नकर्मकृत्॥
karmaṇy akarma yaḥ paśyed akarmaṇi ca karma yaḥ, sa buddhimān manuṣyeṣu sa yuktaḥ kṛtsna-karma-kṛt
Translation
One who sees inaction within action, and action within inaction, is wise among people. Such a person has, in truth, understood how to work.
Busy isn't the same as effective. Learn to tell the two apart.
What does this mean?
There's busywork that accomplishes nothing, and there's quiet stillness that accomplishes a great deal. This verse points at the difference and says real wisdom is being able to tell them apart.
In simple words
Krishna says the wise person can spot when a lot of busy activity is actually accomplishing nothing, and when apparent stillness is doing a great deal. Being able to tell those two apart is what he means by really understanding how to work.
The deeper idea
The verse plays with the words for action and inaction to break the assumption that visible motion equals productivity. Frantic activity driven by ego or anxiety can leave nothing behind. A calm, unattached person can be fully engaged and, in the sense the Gita cares about, not be doing anything at all, because they're not entangled in it. The wisdom being praised is discernment: seeing what a given effort is actually made of, rather than judging by how busy it looks.
How it applies to life
Think of a workday spent answering messages and sitting in meetings where, by evening, nothing real moved. Then think of an hour of quiet, focused thought that actually solved the problem. The first looked like work and wasn't. The second looked like idleness and was the whole job. This verse is the reminder to measure by what's actually shifting, not by how full the calendar was.