This is the conventional wisdom, but in my n=1 experience, I have never seen the “ideal case sequential development” actually work in the wild.

The ideal case presumes that everything is known when the sequential development is planned, which is what permits it to be optimized.

But in my n=1 experience, everything is not known, the development team is constantly discovering new information, requirements change, and the ideal plan never works out as originally envisioned, whether we tried to develop sequentially or not.

But the “ideal” plan is often like highly optimized code: Expensive to change. So it has its own cost that cannot be escaped. So I am left extremely cynical about the “ideal sequential development” approach.

It always seems at the outset to be cheaper and faster, but ends up being expensive and inflexible.

JM2C.

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Now if you want something REALLY expensive, I give you “Scrumfall,” a plan where you combine the costs of iterative development with the inflexibility and attendant costs of fixed date, fixed scope, and attempt to optimize sequential development.

But hey, you get to wear an “agile” badge, even though “inspect and adapt” has no place in the process.