No, what he's saying is that engineering is about tradeoffs. Adding another framework introduces another node in the graph, and n edges. If you don't need fancy authentication and are pretty confident you never will, then don't add devise. If you don't know or understand why you would use some bleeding edge web server or framework, use what is well-understood and has the least moving parts.

Leaning on the code of other people is something you do very deliberately, and it's a mistake to think that it always saves you time.

If you think you're saving yourself from reinventing wheels by adding Yet Another Gem into your gemfile, then you'll quickly find yourself constrained by the code of other people instead of your own code and mental model.

Your app becomes a mat woven of interdependent Things That Almost Do What You Want and you'll spend more time wrestling with other people's code than the time it would've cost you to write and maintain exactly what you needed in the first place and no more.

It's sort of like that time you thought Devise was going to save you all this trouble but soon realized you merely moved the battlefront from (A) a diff'able domain that you control to (B) Google SERPs, Stack Overflow answers, and a Github wiki page of customization boilerplate and copy-and-paste'able incantations that sorta do what you want.