what does ” i have seen so much more than you know” mean?

I have heard older people say this when they are talking to a younger generation that think they know everything. The older people are putting the younger people in their place.

I have also heard this expression used by a soldier… Ex.. The soldier says I have seen much more than you know.. Meaning they have seen it first hand and what you hear on the news is sugar coated.

i would tend towards the first interpretation.

it fits the ominous tone in which the phrase is usually uttered, and it would rid the utterer of the necessity of further self explanation, putting his insight and his motives beyond even the possibility of comprehension on your part, without blaming you for it, thus avoiding to rouse your adversarity.