This question relates to genome sequencing using the shotgun method.
When presented with the sequence contigs, I was taught that to fill in physical gaps between contigs, we can use PCR.
"Pairwise combinations of contig end primers can be used to PCR the organism's genome. An adjacent pair of primers will give a PCR product of the size of the gap between them."

However, why is this? Why do adjacent pairs of primers give a PCR product, but non-adjacent pairs of primers would not?

My understanding is that the pairs of short primers we using are both complementary to a single strand of DNA from the organism's genome.