* The simpler the interface for the user, the more decisions you can make behind the scenes. A good example here is "git push heroku". Not only is that something every user (bot or human) can run, it is also easy to script, protect, and scale. It keeps the surface area small and the abstraction makes the most sense. The code that was behind that push lasted for quite some time, and it was effectively 1-2 Python classes as a service. But once we got the code into our systems, we could do anything with it... and we did. One of the things that blows my mind is that our "slug" (this is what we called the tarballs of code that we put on the runtimes) maker was itself a heroku app. It lived along side everyone else. We were able to reduce our platform down to a few simple pieces (what we called the kernel) and everything else was deployed on top. We benefited from the very things our customers were using.
* NOTE: This one is going to be hard to explain because it is so simple, but when you start thinking about system design in this way the possibilities start to open up right in front of you. The idea is that everything we do is effectively explained as "input -> filter -> output". Even down to the CPU. But especially when it comes to a platform. With this design mentality we had a logging pipeline that I am still jealous of. We had metrics flowing into dashboards that were everywhere and informed us of our work. We had things like "integration testing" that ran continuously against the platform, all from the users perspective, that allowed us to test features long before they reached the public. All of these things were "input" that we "filtered" in some way to produce "output". When you start using that "output" as "input" and chaining these things together you get to a place where you can design a "kernel" (effectively an API service and a runtime) and start interacting with it to produce a platform.
I remember when we were pairing down services to get to our "kernel" one of the Operations engineers developed our Chef so that an internal engineer needed maybe 5-7 lines of Ruby to deploy their app and get everything they needed. Simple input, that produced a reliable application setup, that could now get us into production faster.
Anyways, those are just a couple.
https://theapplewiki.com/wiki/C4000