As someone who does this for a living, I agree. Know what that hard part is and attack it right after the basic infrastructure and connectivity. Reconciling th

As someone who does this for a living, I agree. Know what that hard part is and attack it right after the basic infrastructure and connectivity. Reconciling those external transactions is just one bar of the overall piece, but it's a doozy. As another post points out, you need a lot in place to work out what is wrong when things go wrong, logging, reporting, lots of fancy sql queries to show what is happening. Unless you have done one of these, you would think that once you a fault tolerant stack that implements a fast switch and pattern matching you are up and running. DK strikes again. Focussing on that stuff means you have not realised the hard bits yet. The music is good example. You play the piano well and when you face a challenging piece you don't even know know enough to understand what bits are hard. The master says, "look at this bit one hundred times over and you might get a feeling for what you don't know".