यया स्वप्नं भयं शोकं विषादं मदमेव च।न विमुञ्चति दुर्मेधा धृतिः सा पार्थ तामसी॥
yayā svapnaṃ bhayaṃ śokaṃ viṣādaṃ madam eva cana vimuñcati durmedhā dhṛtiḥ sā pārtha tāmasī
Word by word
The verse says
The steadiness by which a dull-witted person will not let go of sleep, fear, grief, low spirits and conceit: that steadiness, Arjuna, is dark.
In plain words
The third kind, and it is a sly piece of writing.
This is still called steadiness. The person is persistent, consistent, utterly reliable. What they are reliably holding on to is sleep, fear, low spirits and self-regard.
The faculty is working. It is clamped onto the wrong things, and it will not let them go.
Where you've felt this · in failure
Your father's colleague has told the same story about being passed over for a promotion for eleven years. The details have not changed. He can produce it on request. Whatever else happened in those eleven years, that one account of himself has been kept up with perfect consistency.
Going deeper
Persistence applied to a grievance is still persistence, and seeing that is the point of calling this steadiness at all.
It would have been easier to describe this person as weak. The verse does the opposite. It credits them with the same faculty as the man on his twenty-year walk, and notes only what it has fastened onto.
This is oddly encouraging. If the capacity to hold on for a decade is already present, nothing has to be installed. The machinery works. It is pointed at a grievance, a fear or a story about yourself, and it is maintaining those with great fidelity.
Which reframes the question for anyone who thinks they lack discipline. You almost certainly do not. Look at what you have maintained without fail for ten years, including the things you would rather not have maintained, and you will find the steadiness was never missing.