1. Introduction

In the discourses on the Bhagavad Gita in Tamil, Swami Omkarananda, in his explanation of the Shankara Bhashya for the chapter on Karma Yoga, says, that the biggest hurdle that people face to embark on yogic practices, especially those that yield the most benefit, is the fact that most of the fruits of yoga are "Adhrishta"(अदृष्ट) , which means that they cannot be easily seen in this lifetime. For example, the definition of yoga, according to Vyasa, is samadhi, a state free of mental disturbances (chitta vrittis). However to get to this state one needs to sit in meditation daily, which is a very difficult task for most people. The same holds for other powerful yogic practices like fasting (tapas), restraining of the senses (Pratyahara), study of scriptures (Svadhyaya) and Ishwara Pranidhana (Surrender to the divine), all of which are supposed to yield great powers according to the yoga sutras but the results are not tangibly seen in a short period of time. 

Many people find yoga through asana practice. They are attracted to the aesthetics of toned bodies and the ability to flex them into various shapes. Through asana practice, some people, then discover certain refined states of mind associated with lifestyle choices, in particular a clean and light diet, early morning routines etc. Their curiosity then prompts them to delve more into the ancient scriptures and they develop intuition and trust in the lifestyle choices mentioned in those scriptures, even though they may seem difficult at first. For others, yoga just remains an exercise routine. So, how is it that some people are able to embark on these practices even though the fruits are not easily seen in this lifetime while others don't ?

श्रद्धावीर्यस्मृतिसमाधिप्रज्ञापूर्वक इतरेषाम् (1.20)

śraddhā-vīrya-smr̥ti samādhi-prajñā-pūrvaka itareṣām

Chandogya Upanishad (1.1.10) says that yogic practices done according to the scriptures with knowledge and Shraddha result in great power.

यदेव विद्यया करोति श्रद्धयोपनिषदा तदेव वीर्यवत्तरं भवति

What is done with knowledge, Shraddha (deep faith), according to the principles of the Upanishads (i.e. yoga) results in great power.

So, how do you develop Shraddha or is it possible to develop it at all ?

3) Seen and Unseen life experiences (Dhrishta, Adhrishta Janma Vedaniyah)

The yogic texts say that one's samskaras (latent impressions) determine whether one has faith in undertaking certain endeavors (Ref: Vasanas and Samskaras: The "smell" of latent impressions ).

ततःतत् विपाकाणुगुणानाम् एव अभिव्यक्तिर् वासनानाम् (Yoga Sutra. 4.8)

Tatah tat Vipaka Anugunanam eva Avibhyakhthir Vasananam

From these (three types of Karma), only those Vasanas fructify which have favorable conditions to manifest.

The actions done due to these vasanas then cause seen and unseen (in future births) life experiences (with kleshas as the root cause causing left over desires in the form of Samskaras or imprints)

क्लेश मूलः कर्मशयो दृष्ट अदृष्ट जन्म वेदनियः  (Yoga Sutra 2.12)

 klesha-mula karma-ashaya drishta adrishta janma vedaniyah

The Bhagavad Gita goes into great detail to explain how a person who starts off on the path of yoga, even if they should slip in a lifetime, will find yoga back in a future life time (Ref: Once a yogi always a yogi). This is where the Shraddha comes from, from deep laden imprints with a firm conviction that these practices will yield fruit in this or a future lifetime. 

पूर्वाभ्यासेन तेनैव ह्रियते ह्यवशोऽपि स: |

जिज्ञासुरपि योगस्य शब्दब्रह्मातिवर्तते || Bhagavad Gita 6.44||

"By virtue of the past practice (the yogi) is again attracted to yoga; Even one who merely wants to know about yoga goes beyond the word-Brahman (the all pervading one)."