The more years I've been developing software (and it's been awhile) the more I come to find that the answer is almost always "it depends". The definition of "simple" depends on the case, the requirements, and the level of uncertainty about the future. The definition of "complex" depends on the case, the requirements, and the level of uncertainty about the future.
I've run into a lot of situations where doing the "simplest thing that could possibly work" ultimately led to mountains of pain and failure. I've also run into situations where things were over-engineered to account for situations that never came to be resulting in similar pain.
It boils down to "it depends" -- a careful analysis of the requirements, tradeoffs, future possibilities, and a mountain of judgement based on experience.
For sure, err on the side of "simple" when there's uncertainty but don't be dogmatic about it. Apply simple principles like loose coupling, pure functions, minimal state, avoid shared state, pick boring tools, and so on to ensure that "the simplest thing that could possibly work" doesn't become "the simplest thing that used to work but is now utter hell in the face of the unexpected". It all depends.
I've run into a lot of situations where doing the "simplest thing that could possibly work" ultimately led to mountains of pain and failure. I've also run into situations where things were over-engineered to account for situations that never came to be resulting in similar pain.
It boils down to "it depends" -- a careful analysis of the requirements, tradeoffs, future possibilities, and a mountain of judgement based on experience.
For sure, err on the side of "simple" when there's uncertainty but don't be dogmatic about it. Apply simple principles like loose coupling, pure functions, minimal state, avoid shared state, pick boring tools, and so on to ensure that "the simplest thing that could possibly work" doesn't become "the simplest thing that used to work but is now utter hell in the face of the unexpected". It all depends.