There are a few things in life that you just have to do. For some it's eating. Others feel compelled to breathe on occasion. Para moi, the compulsion is writing.
If I discipline myself or am forced by circumstance the itch may be held at bay for days, maybe even weeks. Take school for instance. Robbed of my free time, I haven't been able to write properly for weeks. Today the itch became to strong to resist. Abandoning my studies for midterm exams tomorrow, I've broken down and started writing.