Well, perhaps you are right, NJ, but I venture to suggest that your own circle of friends is, even if we're being optimistic, not a lot when compared to 17 million. It's unlikely, then, that they have captured the full subtlety and diversity of the Brexit camp.
Now, having said that, anyone taking polls seriously would have seen that the UK has been pretty much evenly divided on the EU question for -- well, decades. So it probably is true that most people knew how they were going to vote when the opportunity arose. The point is that this neglects the other large chunk, the undecided, and that any campaign will have been targeting them. The winning side only needed to come ahead on that lot, and apparently succeeded in doing so.
Campaigns are important not because they shift loads of people's opinions but because they shift just a few -- but just a few is often all that's needed.