Most modern politicians are great tacticians but lousy strategists. They spend huge efforts on planning the run-up to the next election, but they don't often think about the longer-term consequences of their actions (presumably because they don't expect to be in power for that long anyway).
However, the SNP and the wider independence movement are a great exception to the rule. Until very recently, nobody joined the SNP because it was a smart career move, but because they wanted to make Scottish independence happen.
I think this explains why most Unionist politicians have been so bewildered by the independence referendum. They assumed from the outset that the SNP wanted a referendum because they thought it'd be a smart tactical move, not because they actually thought it was the right thing to do.
As this excellent (but long) article argues, David Cameron agreed to the referendum because he thought it would tactically be a good way to shut up the SNP. (However, this tactic failed because he agreed to holding it in 2014, giving the Yes campaign plenty of time to convince the voters.)
The focus on tactics also explains why Unionist politicians so often talk about the short-term costs associated with independence. Of course independence is likely to be a very bad tactical move -- within the first couple of years, the costs are very likely to outweigh the benefits.
However, as soon as we start looking further ahead, the transitional costs will be dwarfed by the huge financial and social benefits associated with independence.
The Unionists keep staring at the immediate costs and don't understand why people aren't scared. Meanwhile, the independence movement is full of people with strategic sense who can see why independence makes perfect sense as soon as you take the slightly longer view.