NATO is overly dependent on ISR (i.e., Intelligence, Surveillance and Reconnaissance) platforms that can tell you where troops and equipment are situated but cannot discern the capabilities and morale of the Russian troops. Russia enjoys a lopsided intelligence advantage. Russian ISR capabilities are at least equal to anything the West has, but it has other Aces to play that NATO does not. Russia has ample human sources planted in NATO and Ukrainian military headquarters and units and knows what Ukraine is planning to do and where it intends to mount its attacks. That kind of robust human intelligence is invaluable
Even if Ukraine manages to pull off a surprise attack in an undefended sector along the Russian defensive lines, Russia has the logistics in place to deploy forces and staunch any breakthrough. Russia has at least 10 times the number of troops available to throw into any breach that Ukraine tries to exploit.
