I often heard that comment saying armed civilian resistance is no match for a modern military but history and present day events show us it can be very effective. Not everyone in a populace are going to be against the government therefore the military cannot deploy all their ultimate weapons without destroying their own country and loyal citizens.
The modern military might has had no joy in any country where it has been supporting a government and loyal citizens against rebel forces, you can list them one after another where ultimately outside military forces have had to pull out as the cost to man and machine has been too much for little gain.

Countries left to their own devices i.e. civil war, ultimately end up with a government, democratic or dictator, who appeals in popularity to the majority, or come to a deal with the other side and lay down arms.

An outside military force is only successful against a country or state once a declaration of war is made and then all weapons and techniques can be brought to bear against the entire enemy country.

The armed resistance movements usually with minimal training and weaponry in the European countries involved in the second world war were very effective against probably the most well armed, trained, prepared and determined enemy. Disrupting military supply lines, intelligence, etc., is very effective against any military. Of course nowadays there are enough civilians around that can construct weapons up to and including nuclear devices if they want to.

In regards effectiveness of military, I always remember an area we use to hunt deer in up one of the big rivers in the Canterbury high country. We used to trail bike in, had a hideaway bivvy built with access through swamp and tucked in under a terrace in scrub country. We would evening shoot and then spotlight all night in the National Park. One trip we came across an army unit undertaking exercises in the area and camped right next to our bivvy access way. We did a roundabout route to the bivvy, set up then headed out for the evening and night. Got a few deer and ran into the army boys on the way back to camp. They were bemoaning the fact they had tried to get a deer (ambushing in their words) but just couldn't get on to any. Couldn't figure out where we were camped and how we moved around without them seeing us. As armed civilians we could have wrecked some havoc if so disposed.