Everyone wants a withdrawal, the US, the UK and the Afghans themselves want us out. And at the earliest possible moment we will withdraw, but that moment isn't quite yet.
The betting analogy above does not work. Our adventure in Afghanistan is more like an investment. We have spent time and lives getting to a situation where our investment might pay off. We wanted a western friendly government installed instead of a anti western fundamentalist Islamic dictatorship which was there before. The Khazi Government whilst not perfect, is pretty close to what we want. However, it is not quite strong enough to support itself. We need to hold our nerve just a little longer before our investment matures and we can get what we want. There is an element of chance like betting, except we have fought long and hard to get the odds strongly in our favour.
There is no one more opposed to the Afghan war than me, but we need to see it through if the whole thing is not to have been pointless.