Why Sea Lion needs more than a landing plan

What would make a successful Operation Sea Lion so difficult?

German forces would face concentrated naval opposition, mines and aircraft, then prepared coastal and Home Guard defences, so a viable scenario needs extensive additional assumptions.

Operation Sea Lion faced a layered defence rather than a simple Channel crossing. R-class ships, Nelson and Rodney, destroyers, aircraft, and minefields could attack the invasion force before it reached shore. German troops who landed would then meet regular forces and a highly motivated Home Guard. Fuel-based coastal defences could cover the water and beach in a combustible mixture, then ignite it after landing craft began unloading.