If you take the world location of the arrow as start and the target location as end for the trace it will draw a line from the arrow to exactly the location of the target.
What we want is to add more distance to that trace. Shoot through our target point so to speak.
Shoot From is where the trace will start. We take that location and get the rotation needed to point at the target location. Now that we have a direction we can take the forward vector of that rotation and multiply it by a distance… How far in that direction do we want to trace. Then add that vector to the shoot from vector to give us a shoot at vector.
