प्रयोजनमनुद्दिश्य न मन्दोऽपि प्रवर्तते

प्रयोजनं सम्प्रवृत्तेः कारणं फललक्षणम् ।

प्रयोजनमनुद्दिश्य न मन्दोऽपि प्रवर्तते ॥ 

श्रीमच्छङ्करभगवत्पूज्यपादविरचितः

सर्ववेदान्तसिद्धान्तसारसङ्ग्रहः

prayojanaṃ sampravṛtteḥ kāraṇaṃ phalalakṣaṇam ।

prayojanamanuddiśya na mando'pi pravartate ॥ 11 ॥

śrīmacchaṅkarabhagavatpūjyapādaviracitaḥ

sarvavedāntasiddhāntasārasaṅgrahaḥ

The above quote in various forms is available in many texts and many texts on Dharmasastrams

The above slokam comes in Sarvavedanta Sara Sangraham of Shankara in the part.. Sadhanachatushtayam

The reason for embarking on any human activity is with the expected result in sight.

Without any result or utility in sight even the dull headed persons would not embark on an activity.

For any activity, there should be an aim, and there should be a reasonable expectation of achieving such result.. Without any use or purpose in sight, no one, even if he is dull headed would ever engage himself in any activity..

Of course, there can be fallacies in the expectations, in the way the activity is pursued, and the projected results. And the result might not be as effective as expected.. But without an expectation no one would do any work..