I spent the day helping my folks with a garden project -- fencing in a chunk of the garden to keep the critters out. We needed to trench 24" deep for the posts and the portion of the wire fence that would be below ground.
In planning this out, I had recommended to my mom that she rent a mini excavator from the local hardware store (yes, they have a backhoe, but there were a bunch of elements of the job that made a 360° tracked machine a better choice). Someone at the store convinced her that a trencher (picture an over-sized chainsaw on wheels) would do the job just as well, and cost half as much to rent.
So, we started digging with this trencher. Bottom line: surface was too soft, ground was too rocky. The machine got hopelessly mired on it's first pass and I had to tow it out with my pickup truck. Our second pass fared just as badly. My dad and I looked at this and said no way. Of course, by then it was nearly noon.
I hustled my butt down to the Nursery, fetched the dumptruck and trailer, ran over to my place, loaded the backhoe, and got myself back to my parents' place in an hour. I spent the rest of the day digging and setting posts...