You also work in a place where it is not acceptable to be performing a task for the first time, as they are of importance enough to require prior experience, and hence usually do not evolve quickly. Software is constantly changing and software developers are much more likely to completely overhaul a product than a physical design. They will also deal with changing dependencies due to updates and, in things like Javascript land, what way the wind happened to blow that day. Software developers are constantly on adapting and uneven ground for most products which strive to keep very up to date.

At places where true software engineering work is required, like mission critical systems, the type of planning that you may be used to will be more common. However even for large companies like Oracle, things like the healthcare site can go wrong [1]. That is just the nature of having to constantly adapt. If things just stayed stagnant, we could get the same level of safety and generations of consistent improvement that things like cars have received, which does happen with maybe Unix or C perhaps. But that does not change the fact that most day-to-day software development is all about hiring someone who knows slightly better than you, but, more importantly, knows how to learn how to get many reasonably new things done which involve parts of what he knows. We don't have the luxury of using safety or danger as a warning, usually.

[1]: http://www.bizjournals.com/sanjose/news/2013/12/03/cover-ore...