Well I just re-entered the hobby after quitting some years before.
My first tank I made to many mistakes as I didn't know quite what it would take. I had a light fixture that could grow algae well but not plants for instance. Thought doing DIY CO2 would be enough, but it wasn't and my plants still looked sad. Then I changed the substrate to something more nutrient rich, still not enough. And other problems cropped up along the way like a pest snail invasion I couldn't eradicate.
I'd say the main reason I scraped that first tank and quit was that I was to focused on what I eventually wanted it to look like, the end result, and didn't relax and enjoy the process. That plus too many mistakes in the beginning and was slow to realize it, so it was frustrating to see my plants doing so poor.
This time I've done a lot more research upfront, and I'm plunking more money down on things that will make the upkeep simpler and more enjoyable. Before I did water changes with buckets (I must have been crazy), now I have a python. Going pressurized timed CO2 instead of DIY, getting two Fennix LEDs so I'm not limited by light, etc.