Srimad BhagavadGita

The knowledge about karma yoga will be imparted by Kṛṣṇa starting from the next śloka. Before doing so, Kṛṣṇa talks about its greatness in this śloka. Before telling about something, if its greatness is explained, then the resolve to practise it strengthens. Hence, in this śloka Kṛṣṇa distinguishes the greatness of karma yoga over other ordinary karmas. HE says, "In the practice of this karma yoga, there is no wastage of effort that is put in or any negative impact when left in between. Even a little practice of karma yoga provides protection from great fear."

iha (In this practice of karma yoga) 

abhikramanāśaḥ nāsti Even if karma yoga is discontinued after starting it, there is no wastage of the effort that was put in. Efforts are said to be wasted when the effort invested does not fetch any reward. This means that, even if someone who starts practising karma yoga discontinues the practice in between due to unfavourable conditions, in future he can pick up the practice from where he left and avail the complete benefit upon its completion. This implies that no effort from the beginning gets wasted.

pratyavāyaḥ na vidyate Even if the practice of karma yoga is stopped in between, one will not receive any negative result. 

asya dharmasya svalpamapi mahataḥ bhayāt trāyate Even a small portion of this practice protects us from the mighty fear of saṃsāra. We see that when worldly or vedic practices followed for material gains are discontinued in between, all the efforts put in until then get wasted and negative results are additionally incurred as penalty. The specialty of this karma yoga is that, even if it is discontinued in between, it delivers results in the course of time when it is continued from the point where it was left and does not incur any penalty for the discontinuity too. This has been explained in detail in śloka 6.40 Pārtha! naiveha nāmutra vināśa stasya vidyate (Arjuna! There is no destruction for him in this world or the next, there is no ruin either in the form of failure to attain one's goal or in the form of attainment of undesirable results because of defects in the performance of works). Every individual has obligatory daily (nitya) and occasional (naimittika) duties based on his class and stage in life which he must perform. Lapses in their performance might occur due to the individual's incapability or unfavourable conditions . Only when the individual skips the duties knowingly without any reason will they cause harm or fail to give results. Contrarily, in the case of kāmya karmas (fruitive activities), even if a minute portion of the procedure gets left out, they not only fail to give the desired result (eg. stay in heaven upon leaving this body) but also cause negative results (like becoming a brahma rakṣasa upon leaving this body).