Good theology should form a tight logical system. Different doctrines fit together, and partially explain one another, to make a cohesive picture. Bad theology often has holes left in it where different doctrines do not dove tail in logical ways with other doctrines.
Just because a doctrinal system is tight doesn’t mean it is correct. Human creativity and demonic false religion are both capable of forming tight systems of theology. Nevertheless, if your theology has gaps you should study to either close the gaps or adopt a more correct system.
One of my favorite places to demonstrate two doctrines that fit together well is the virgin birth and original sin. Paul teaches us that sin is passed down from the father’s side. The virgin birth described by Luke teaches us Jesus had no father other than the heavenly Father. Therefore putting the two ideas together, Jesus had no earthly father passing down original sin to Him. This is necessary since He was God’s perfect Lamb. If He had original sin, He would not be sinless or able to be our perfect, once for all, sacrifice.