Nobody knows what they're voting for.
If the Yes vote triumphs, nobody knows what the result will look like.
* For starters there are the big issues like currency, EU, relationship with rUK on matters like defence etc. There's an awful lot of horse trading to be done, nobody knows what the outcome will be, but one thing that seems pretty certain is that nobody will get everything they want.
* Then there's the fact that nobody knows what an independent Scotland would feel like. In 20 years time, would everybody be complaining that the country was being run for the benefit of the bankers and the chattering classes in Edinburgh? I would hope not, but nobody knows. A fact of life with any parliamentary democracy is that you never really know what the government will do in the 4 years or so between the rare occasions when they have to listen to the voters.
* And finally (for me now, though there may be other aspects I've overlooked), nobody knows what scars would be left if the vote is narrow. If the result is, say, 55-45 - which would be a landslide compared to current polls - that's still 45% of the population who will find themselves living in a country in which they didn't want to live. That's bound to have some effect, but it's impossible to predict what it would be.
And if the No vote triumphs, again nobody knows what the result will look like.
* The reaction of the Westminster government is impossible to predict. There are those who believe that a close vote would lead to greater devolution for Scotland. There are those who believe exactly the opposite, that the Westminster government would arrange matters so as to reduce the chance that the Scots could ever try this again. It could go either way, but it probably won't be pretty.
* And again, nobody knows what damage a close vote would do to the fabric of the country. If the result of a close No vote is a clampdown from Westminster, powers taken away from Scotland, less uniquely Scottish institutions and so forth, how will that affect relationships within Scotland? Nobody knows.
Nobody knows what they are voting FOR in practical terms. At the end of the day it all comes down to principle, hope and belief, that Scotland will be better off somehow (for some personal definition of "better off") if it isn't - or is - part of the UK. Voters in both camps may find that they're facing a Pyrrhic victory - that they've won the point of principle, but eventually find that the mundane practicalities are worse than before.