The practice of law is a demanding profession. Lawyers often are highly-motivated individuals, driven to serve clients and succeed in matters. They typically are engaged in adversarial relationships with other lawyers (whether in litigation or transactional matters), and measure their lives in tenths of an hour.
In such a demanding, high-stress industry, sometimes lawyers take on too much. The legal market is highly competitive, so lawyers may feel that if they do not prioritize their career, they may fall behind.