यः शास्त्रविधिमुत्सृज्य वर्तते कामकारतः।न स सिद्धिमवाप्नोति न सुखं न परां गतिम्॥
yaḥ śāstra-vidhim utsṛjya vartate kāma-kārataḥna sa siddhim avāpnoti na sukhaṃ na parāṃ gatim
Word by word
The verse says
Whoever throws out the measure the scriptures give and acts on impulse instead reaches nothing finished, no happiness, and not the highest place.
In plain words
A measure from outside yourself, is the argument.
Śāstra-vidhi - the rule the old texts lay down. Not because old books are magic. Because the alternative is named in the same line: acting as desire moves you.
Those are the two options on offer here. Something tested by many people over a long time, or whatever you feel like this morning.
Where you've felt this · in creative work
A young musician decides that scales are for people without talent, and plays only what comes to him. For a year it sounds free and interesting. Then he sits in with others and finds he cannot follow a key change, and the pieces he writes all turn out to be the same piece. He was not wrong that rules can trap you. He had just thrown out the ones that were holding him up.
Going deeper
An outside measure is being argued for here, and the argument is not that old books cannot be wrong.
Śāstra means the tested teaching. Setting it aside is paired in the same sentence with acting as desire pushes you, and that pairing is the whole claim. Not: obey, because it is written. Rather: if you discard the measure, look honestly at what will be doing the measuring instead.
That is worth sitting with, because the modern instinct is that following your own sense of things is the braver choice. Sometimes it is. But the people described across this chapter were doing precisely that, every one of them sincere, and not one of them able to see it from inside.
Which is the real use of anything outside yourself - a book, a teacher, a friend who will say the unwelcome thing. Not authority. A second opinion from somewhere your own appetite is not already sitting.