"Excessive availability can become a problem because now it’s the expectation. Don’t make your system overly reliable if you don’t intend to commit to it to being that reliable."
What most people don't realize is that you will get more OOMs if you disable overcommit.
New services may be launched with provisional technology to establish or evaluate a market or pricing model. The underlying technology in the initial implementation may have different performance or availability characteristics to what's actually envisioned for the full-scale product, and care has to be taken to actually compensate for this - i.e. introducing synthetic delay/jitter/faults to avoid setting the wrong expectation for the product.
Wrong guess imho. It means building highly reliable systems requires knowledge and experiences. Trying to build them and solving the problems step-by-step is one way to understand how it can be achieved.