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you're using the Go SDK, and it's the way Go is designed https://blog.golang.org/error-handling-and-go the error itself is the result of the call to the cloud provider API, it gets stored as an error type. So let's say you try and create a resource, and something goes wrong - you need to check the error explicitly (as per the go design)

I've used go before, my question was more about what actual api calls were happening as my program is run by pulumi

You are right that there are many errors that might not be reported synchronously - like failures from the cloud provider trying to create the resource you specify. But there are also errors that might happen synchronously, for example the inability to register the resource or even some classes of early validation of resource inputs. In general though, it is rare to have synchronous errors from NewResource calls.