Passage Summary: Damaged nerves can grow back slowly, but they need a 'tube' to show them where to go. If the nerve takes too long to grow through that tube, the tube falls apart, and the nerve can't finish the job.

Reasoning: Nerves grow slowly (1mm/day), and the path (sheath) they need to follow disappears if the nerve doesn't reach it within about 90 days.

Analysis: This is a synthesis task where we must combine the provided facts. We know nerves grow at 1mm per day and that the 'guide' (the sheath) disappears after about 3 months (roughly 90 days). Mathematically, this implies that if a nerve has to travel significantly more than 90mm to reach its destination, the sheath will likely disintegrate before the nerve gets there. Look for an answer that draws a conclusion about the distance a nerve can successfully regenerate based on these time and speed constraints.