That brings back the title of the article.
Beginners aren't making distributed systems on legacy 32 bit hardware (microcontrollers?) that max out a 32 bit space.
Really the article needs to bifurcate into
1) Actual mistakes beginners really make, like sucking entire tables over the network into local arrays and then hand writing a (slow and buggy) emulation of the DB server's JOIN. Bonus points for not memoizing/caching those giant tables. Another beginner comedy is NIH reinventing of the concept of having an index for speed, written entirely in slow application code. Turing complete being what it is, beginners sometimes try to write a rational database manager in their application code, not knowing if its really handy and could cut down on round trips and bandwidth, someone probably added that to the RDBMS code back in 1990. Another mistake beginners make is scaling, designing a 1E9 system for a 1E3 problem or vice versa. Another mistake beginners make is thinking some web post from '96 is relevant because nothing has changed since then (like storage and speed and application load) vs ignoring other posts from '96 because this time really nothing has changes since then (like basic computer science concepts), or rephrased 90% of the web should be ignored and beginners will ignore the wrong 90%.
2) Things beginners do that sounded like a great idea like not normalizing their data that turn into a 3-ring circus of writing convoluted application layer code to work around it. Sometimes you can write hundreds of LoC to avoid each line of SQL. Or getting into a habit of writing "baby's first todo app" using small 32 bit ints and then blowing it when they move up in the world into giant distributed systems.