I am living both, 1+ more years to ER in a 30+ year career in Corp America, and have run a "basement business" since 2003. I have a hobby in vintage German cars and started a business making some restoration parts for them. Parts for the very oldest of cars, a product/market so small that none of the big parts suppliers want any part of. I built all my own tooling, wrote installation instructions, built a website, etc. I source materials from US and non-US companies and outsource parts of the fabrication. I also restore some very expensive and hard to find electrical parts. Virtually all of my business is word of mouth within the car hobby now.
It has been loads of fun and taught me so much about business in general even if on a micro level. Materials sourcing, stocking, advertising, customer satisfaction, etc. Some of my parts are in cars that have sold for nearly $200k within the hobby market. The motivation? (besides I like doing it) It is all gravy money. It doesn't figure into our household budget at all. I have taken many trips, bought many things, more old cars, and given my wife many things from that fund. I will definitely keep doing it after ER, but it will never be something that I HAVE to do.
Corp life is not what it used to be, but I am hanging in there. I don't hate my job, and work with some wonderful people, but I will have no problem walking when that day comes (pension eligibility and a boosted "lump sum" offering). I have been very fortunate to this point, paid well, and survived many layoffs, re-structures and 2 company spinoffs/buyouts.