It's one of the shortcomings that I've come to loathe in nginx's declarative configuration language (and also other software products - Apache httpd is just as guilty). Everything just looks so innocent - but the devil is often in the details. So much implied nuance that you have to keep in mind when reading and especially when writing it.

Sure it's expressive and also convenient (the latter at least as long as your configuration stays relatively simple), but something like varnish's imperative VCL that offers very little built-in magic sure is easier to reason about. I have come to consider that a feature.