I really dislike parsing not validating as general advice. IMO this is the true differentiator of type systems that most people should be familiar with instead of "dynamic vs static" or "strong vs weak".

Adding complexity to your type system and to the representation of types within your code has a cost in terms of mental overhead. It's become trendy to have this mental model where the cost of "type safety" is paid in keystrokes but pays for itself in reducing mental overhead for the developers. But in reality you're trading one kind of mental overhead for another, the cost you pay to implement it is extra.

It's like "what are all the ways I could use this wrong" vs "what are all the possibilities that exist". There's no difference in mental overhead between between having one tool you can use in 500 ways or 500 tools you can use in 1 way, either way you need to know 500 things, so the difference lies elsewhere. The effort and keystrokes that you use to add type safety can only ever increase the complexity of your project.

If you're going to pay for it, that complexity has to be worth it. Every single project should be making a conscious decision about this on day one. For the cost to be worth it, the rate of iteration has to be low enough and the cost of runtime bugs has to be high enough. Paying the cost is a no brainer on a banking system, spacecraft or low level library depended on by a million developers.

Where I think we've lost the plot is that NOT paying the cost should be a no brainer for stuff like front end web development and video games where there's basically zero cost in small bugs. Typescript is a huge fuck up on the front end, and C++ is a 30 year fuck up in the games industry. Javascript and C have problems and aren't the right languages for those respective jobs, but we completely missed the point of why they got popular and didn't learn anything from it, and we haven't created the right languages yet for either of those two fields.

Same concept and cost/benefit analysis applies to all forms of testing, and formal verification too.