Confusing CPC Section 52(1)(c) - Kya Loge Main Soch Rahi Hoon?

Section 52(1)(c) of the Indian Contract Act is one thing I still can't wrap my head around. It says that when a person, on the faith of the promise, alters his position in the hope of its fulfillment, the promise can be enforced, but only partially. But here's the kicker - only if the person has acted in good faith and not with ulterior motives. Okay, got it. But then comes the part that has me confused - the 'reasonable' standard. Kya reasonable hai, kya nahi? Is it different for everyone? And what exactly does 'good faith' mean? Is it subjective, or is there some objective yardstick? The more I read it, the more I'm convinced it's meant to confuse us. Anyone else struggling with this one?