Absolutely, Oldgreg!
If you have done something n times, you can make a very good estimate for the (n+1)th time. But if you intend to do something you have never done before (and no one else has ever done before), there's a high degree of uncertainty and unexpected things are likely to happen.
Experience is to expect the unexpected – and tag it with a number, improving your estimations. ;-)
Andrea ("Powered by POET")