Of all the encouraging words in the Gita, these may be the most reassuring. On the path of Karma Yoga, no effort goes to waste. Not a single step. And there is no downside — no adverse consequence from trying and not finishing. Even a small amount of practice on this path protects a person from great danger.
Many people hesitate to begin a difficult path because they fear they will not be able to complete it. What if I start and fail halfway? Krishna answers that fear directly: there is no such thing as failure here. Every honest effort counts. Every small act of selfless duty is deposited in an account that never loses value.
A single lamp lit in a dark room changes everything — not because the lamp is large, but because darkness has no defense against even a small flame. Krishna is saying that Karma Yoga works the same way. Even a modest practice of selfless, equanimous action shields a person from the great fears that haunt human life — the fear of meaninglessness, the fear of bondage, the fear of wasted years.