If you are talking core technology then I disagree. My example is Oauth. There are lots of libraries that make it easy to use Oauth, but then what you have lear

If you are talking core technology then I disagree. My example is Oauth. There are lots of libraries that make it easy to use Oauth, but then what you have learned is not Oauth, but some library and how to use it. Libraries can also add a layer of complexity because they are generalized. And finally, what if the service you buy and don't build needs to be modified for some use case that is particular to your application? While I agree that all of these points should be considered in the general case, core technology for your business presents a very different set of considerations.