0 - Old School
Traditional, normal espresso. Average strength and reasonably high extraction thanks to the more developed and soluble roasts.
1 - Exploration
Higher strength, slightly lower extraction. People wanted a little less roasty-ness and more syrupy/textural espressos so they roast a tiny bit lighter and pull their shots shorter.
2 - Differentiation
Low extraction, high strength. People try to differentiate themselves from traditional coffee brands. They’ll roast even lighter and pull excessively short espressos.
3 - Rebellion
Lower strength, super low extraction. “Anything remotely roasty is sacrilege” is the stance here. Underdeveloped roasts that aren’t soluble yield lower strength espressos and maintain the under-extraction of previous.
4 - Frustration
Slightly higher extraction, low strength. This is the all-too-common razor’s edge between roasts that are too light and too dark. Ever had coffee that’s too dark one week and too light the next? Everyone is trying to get more extraction by increasing roast development but but the low strength is highlighting roasty-ness. Very frustrating spiral.
5 - Extraction
Very high extraction, super low strength. After being frustrated by the ping pong match above, the roasters will opt for light rather than dark. Even longer espressos will be pulled to tease out a modicum of sweetness. Roasts are still underdeveloped, so the strength must be super low to accomplish anything.
6 - Excellence
There’s very few people sitting here. But I’m sure you can guess which spot on the graph it is.
With proper roast development, good brewing practises and a healthy compromise between strength and extraction, some people find themselves happily back at 0 (but with a much more delicious end product).
NB - There’s certainly other progressions, but this one is most common in my experience.