Why do the fitness goals I set with clients turn out unrealistic?

Setting a goal that later proves wrong feels like a mistake, but it is mostly just the normal gap between a plan on paper and a real human life. You cannot know everything about someone's body, schedule, and willpower up front. Some goals will miss. That does not mean you are bad at this. The fix is to treat goals as a starting guess you refine, not a prediction you must nail. Set a first target, watch how the client actually responds over a few weeks, then adjust. Goals that are too big discourage people; goals that are too small bore them. You find the right size by testing and correcting, not by getting it perfect on the first try. With your next client, set a smaller near-term goal and plan to revisit it in a few weeks. You are not failing when a goal needs changing. You are doing the real work of coaching, which is adjusting to the person in front of you, not the plan you imagined.