Sometimes You Do Need It vs. You Ain't Gonna Need It. I suppose he is arguing Einstein's make it as simple as possible but no simpler. I look at YAGNI as a filter not a hard and fast design principle. When starting a non trivial project, I sketch out the design and requirements. Then I apply YAGNI to eliminate the cruft and those features that are nice to have but would delay the first release.
SYDNI and YAGNI are 100% complimentary. I just chose the name partly because I think YAGNI gets a disproportionate amount of attention due to having a catchy acronym.
Which life support machine would you rather be hooked up to?
1. A machine whose software developers always did the simplest thing possible
2. A machine whose software developers went out of their way to anticipate possible problems and planned for each of them
I don't think that is an apt description of what YAGNI is about. I think the choices would be more like:
1. A machine whose software developers always did the simplest thing possible
2. A machine whose software developers went out of their way to abstract the code for possible future expansion, uses a custom rule engine written in a custom domain specific scripting language that is compiled down to XML and finally loaded into an SQL server database cluster with failover support.
To me, that is the kind of over-engineering that YAGNI is all about.
This is a very valid point. However, please bear in mind that I wasn't addressing the application of YAGNI as much as I was addressing the misapplication of YAGNI.
