Back in my early career, the company I worked for needed an inventory system tailored to their unique process flow. Such system was already in development and was scheduled to launch "soon". A few months went by and I got fed up with the toil. Sat down one weekend and implemented the whole thing in Django. I'm no genius and I managed to have a solution that my team used for a few years until the company had theirs launched. In a weekend. Amazing what you can do when you want to Get Shit Done!

That's fine when it's self-motivated, but it sets a terrible precedent for expectations. Doing things like this can put in management's mind unrealistic expectations for you to always work at that pace. Which can be unhealthy and burnout-inducing.

I worked at a place in love with their ERP system. Some there had been using it 30+ years, since it ran in DOS.

My Excel skills completely blow, and I hate Microsoft with a passion, but I created a shared spreadsheet one long Saturday afternoon that had more functionality than our $80K annual ERP system. Showed it to a few more open-minded employees, then moved it to my server, never to be shown again. Just wanted to prove when I said the ERP system was pointless, that I was right.