The more I learned about "best practices" the less productive I've become. I think it happens because I spend my mental energy on solving the problem in a way that fits those so called best practices instead of solving it however I can in the most robust way possible.
It took me quite a bit time to re-learn to write a code that solves my problems and is inelegant enough that I can jump on it and modify it as my needs change without thinking how to do it elegantly again.
I start to think that the tools must fit elegantly to the domain, the solution built with these tools can only then be elegant. Code can get hard to read and maintain when the way of thinking about a problem doesn't mach well the way of the toolset works. Things get messy when you try to think of ways to make your tools work in a way they are not designed to.
For example, there are some domain specific languages and frameworks for stuff like maths or physics or engineering that work the way the mathematician or physicist or an engineer will think about a problem. If you try to make the code made with these elegant in a sense that it's optimised and nicely structured from software developers perspective, it will be a huge mess and very hard to understand from the mathematician/physicist/engineer perspective.
Therefore, when working on something I find that the most productive AND maintainable code is the one that matches my thought process - no matter how many sins(like repeating myself or writing non-reusable) are commit. Also, optimisation for the sake of the optimisation is evil. Abstractions work well only when they are intended to match the mental model in the solution and are evil when they are made to optimize something(like making it re-usable for all kind of situations).