Bhagavad Gita
16.23

यः शास्त्रविधिमुत्सृज्य वर्तते कामकारतः | न स सिद्धिमवाप्नोति न सुखं न परां गतिम् ||

yaḥ śāstra-vidhim utsṛjya vartate kāma-kārataḥ na sa siddhim avāpnoti na sukhaṁ na parāṁ gatim

Translation

One who, abandoning the injunctions of scripture, acts under the impulse of desire, attains neither perfection, nor happiness, nor the supreme goal.

Interpretation

Scriptural injunctions (shastra-vidhi) represent the accumulated wisdom of sages about what actions lead to growth and what lead to harm — they are the distillation of centuries of spiritual experience. One who discards these guidelines in favor of acting purely on desire (kama-karatah — doing whatever desire dictates) achieves nothing: no siddhi (spiritual perfection or worldly achievement), no sukha (lasting happiness), no param gatim (the ultimate liberation). Desire without wisdom is the most destructive combination. The shastra is the map; desire without the map leads to being hopelessly lost.