One thing i have learned is to always leave room in your invest in my life schedule for the unexpected. I learned this the hard way when one day I made the mistake of not doing just that and my laptop needed to unexpectedly check disk.
I'd given myself just enough time to do my research and write the article. In addition, it took me longer than I had anticipated to do the research work. As a result, I had ended up spending an entire day on something that needed to be submitted way before my actual finish time.
Luckily my customer is a great guy, but I've certainly learned my lesson and have budgeted for extra time since then. Have you ever experienced a similar problem? How did you handle it?