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And, in their quest to make us connect with the characters, they introduce improbably convoluted personal arcs which strain credibility. Stick to case of the week, and make it good.
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Yes, and a sign of a dragged-out, watered-down arc is consequence inertia, where the fallout of dramatic events takes way too long to play out & logical resolution-points are delayed to the point it's absurd. One reason I like short serials (eg. BBC). Paced mercilessly.