At least if it's a library you're not really increasing your chance of failure. Whereas as you add external dependencies, the odds of one of them being down an

At least if it's a library you're not really increasing your chance of failure. Whereas as you add external dependencies, the odds of one of them being down and taking your service with it increases. So you had better thinking about how you handle failure situations gracefully and so on, so the service you call had better be doing something special (e.g. giving you access to some huge dataset) to make it worth that additional complexity.