"You can fix that, right? It's not that hard." My wife's often saying things like that, but I'm always thinking it, too. So I'm also to blame for many of the projects/ideas we get ourselves into around the house.
"I could save lots of money and then amass an arsenal of tools while making countless trips to the home goods store."
"I could make that bookshelf. Why should I pay an arm and a leg for a train table made of particleboard that most likely will fall apart faster than the time it takes my crackers and milk to go soggy?"
"Busting up that floor? No problem."
It's also just what you do, right? Try to fix things, even when they're not really broken. My 3-year-old son caught that bug -- the one that gets you thinking you need to redo, fix or modify something, anything or just take it apart. All valid ways to spend time.
The good thing is that with the exception of personal safely while using power tools, sharp knives and working with electrical and some plumbing, there's no harm done. It's a house or a table, it’s OK if it’s not perfect. Tearing up a bathroom can be a bit scary but the worst thing to happen is you have to call in a contractor. Even I know my limits -- I don't do structural changes to the house without help.
So, then, why do it yourself? The answer for me is because I enjoy doing the work, working with the tools and materials. And when the project is done I get that sense of accomplishment. I also couldn't afford to get some of the work done and we own an old house that need lots of care and upkeep. We also really enjoy the design aspect of upgrading the house, imagining and planning are a big part of the fun. And now that we have it the way we like it, we'll never move. (Fingers crossed!)
What I have learned is that if the only goal was to save money by doing the work myself, it might not be worth it in some cases. Professionals offer speed and quality gained from experience. I always have to know my limits and skill level. Some projects take a lot of time -- time away from family. It works best when I want to do it for the experience and what I can learn and sometimes, yes, save money.