What problems arise if two modules have high coupling?

Coupling means the interconnection of dissimilar modules with each other or we can say, it tells about the interrelationship of dissimilar modules of a system. A system with high coupling means there are strong interconnections among its modules. If two modules are concerned in high coupling, it means their interdependence will be very high. Any changes applied to single module will affect the functionality of the other module.  Greater the degree of change, greater will be its effect on the other. As the dependence is higher, such modify will affect modules in a negative manner and in-turn, the maintainability of the project is decreased. This will further decrease the reusability factor of individual modules and as lead to unsophisticated software. So, it is always desirable to have inter-connection &  interdependence among modules.