After several weeks we realized it needed new soil. Whoever potted it used a very bad soil: it was hard as rock and almost didn't get it out of the pot. Once we had the Yucca in the new soil, it looked happy and started to green and grow new leaves.
But the leaves would get a few inches long, curl up and die. Every one of them. It went on like this for several months, until we were watering it one day and found a very strange mold on top of the soil, a small line of it a couple of inches long.
When we scooped the mold out it smelled very bad: we knew it was over for the Yucca tree and decided to pull it from the soil. It was apparent that this Yucca tree was not taken care of properly from its beginning, and no matter what we did, it would not survive.
It was sad, too, not because we like Yucca trees. It's not a plant that I would buy. But to see something like this happen to it was unsettling. It was an indication of how people have lost their connection with nature, and worse, that they don't care.
I'm glad that we tried to save it. I'm glad that it really tried to survive. Watching it was a testament to the power of nature and, unfortunately, the destructiveness of mankind.