Without such instructions from the company, many of us would probably put the fertilizer spikes near the trunk of a tree or shrub. But trees and shrubs are better served when we place fertilizer at the periphery of their roots, and that coincides with the farthest lateral extent of branches and leaves.
Like trees and shrubs, our ideas have a lateral extent, and our personal drip lines mark where we can explore. We need intellectual fertilizer that lies on the periphery of our current reach of ideas. An influx of nutrients works best at the drip line of the mind. Close in, the thick old tendrils of our neurons are less efficient at creative thought than those thin new offshoots exploring far from a well established trunk. New ideas lie at the boundaries of what we believe, that is, at the drip line.