From Reddit:

When I was using an Amazon Echo, my biggest complaint was that each third party “skill” has a specific voice command associated with it, and any deviation from that syntax would cause Alexa to not recognize what I was asking for (Haven’t used one in about a year, so this may have changed). I always found this frustrating in comparison to Siri, which can make sense of natural language. i.e. Siri can hear “get me directions to…” or “take me to…” or “how do I get to…” and either way it knows you want help with navigation. Apple made a big deal of this capability when Siri first launched.

But with Shortcuts, Siri behaves more like Alexa in that even though the trigger phrases are customized by the user (which is a one-up on the echo), Siri still requires the exact phrase every time.

And:

Remembering one or two custom phrases isn’t a big deal. But if this is the way Apple is going to open Siri up to third party apps, requiring users to remember dozens of specific trigger phrases (custom or not) is, I think, a step backwards for Siri.

First things first, there is a muddying of the waters at work here. The term Siri Shortcuts is associated with the coming Shortcuts app, which lets you build your own custom workflows which you can fire off as you like. You can assign a trigger phrase to a shortcut which, as the Reddit user points out, must be an exact match for Siri to fire it.

If you build a lot of these, you might run into a problem, but this is a problem with an easy solution. Apple maintains a list of all your trigger phrases, in Setting > Siri > My Shortcuts. [H/T Marcus Mendes]

Interesting point, though. I wonder if Siri will eventually be able to “machine learning” its way to an educated guess as to the shortcut you wanted if you are pretty close.