The phrase 'やるならやらねば' carries a sense of urgency and determination that's hard to capture perfectly in English, but 'If you're going to do it, do it right' comes close. This version maintains the original's motivational push while adapting to English phrasing conventions. I remember hearing similar advice from a coach in 'Haikyuu!!' where the characters often face moments demanding absolute commitment.
Another interesting parallel exists in Western business culture with Nike's 'Just Do It' slogan. While shorter, it embodies that same spirit of decisive action. The key difference lies in the Japanese version's implicit warning against half-hearted attempts, which resonates deeply in collectivist societies where unfinished tasks affect group dynamics.