I saw a junior engineer try to add a patchwork of libraries just because he was not confident in his ability to do something correctly, leading to a lot of maintenance overhead that grew very quickly.
Many of the previous frontend engineers got fired from my current company because they did not produce at all - a direct result is a polluted codebase that needs to be scrapped asap because it has led directly to poor perception of product. It also is extremely difficult to iterate upon.
One company I was at had some very terrible legacy code from full stack engineers. The person who wrote the code was fired as well, but not before leaving damage that persisted for years - some triply JSON.stringified JS object, along with some other extra parentheses, was stored right into the database as a string! This meant every time the data had to be fetched, it had to be parsed by the server to fill certain other data, but the core answer object was still sent as it was due to the difficulty associated with sending a parsed form (the backend was Java), which meant that the frontend also had to parse it! Thankfully we were able to silo the damage to an easy to adapt modular service, but it was the cause of much sadness, especially when it was a core piece of data for our product.