I've been pondering about why sometimes progress seems hard to make when I am learning a new piece of technology, which other people apparently just pick up and start using with no trouble at all. I now wonder whether it's a combination of personality and knowledge.
In common with many developers I like to understand things thoroughly. For me this means being able to construct satisfactorily self-consistent mental models that I can, effectively, "unit test" by applying what-if techniques. Unfortunately my history as a developer means that I have a detailed knowledge of system architecture. Without claiming to be fully up-to-date (for example the last time I built logic was in 1987, from Schottky TTL clocked at 12 MHz), when I use the term "full-stack" I include a reasonably detailed knowledge of all aspects of system architecture, including the hardware, operating system, language support libraries and application.
In other words, I am (often subconsciously, thanks to many more than 10,000 hours of practice at this computer game) aware of lots of things that can go wrong at many different levels.
I suspect this causes me, without specific motivation, to choose test cases that go “near the edge of the envelope”. It's frustrating when I'm learning because it often reveals deficiencies (most often in the documentation) of the “system under test” that can block progress; but I also believe it helps to integrate my newly-learned knowledge, and leaves me with valuable knowledge that you just can't pick up in the middle of the road.