Every vote counts
In the 2006 elections Likud won an extra Knesset seat on account of 116 votes. It got 281,996 votes to Yisrael Beiteinu's 281,880. The surplus vote agreement between the two gave the 12th seat to Likud, making Netanyahu head of the opposition and leaving Lieberman with 11 seats.
It may seem the most rational decision possible - not to vote. What difference can one vote make, after all? One Knesset seat requires about 30,000 votes, so what influence can one person have? May as well go to Mt. Hermon and see some snow, or simply stay home "with the tea, the lemon and the old books" (as Arik Einstein's song goes ) and let the suckers stand in line at the polling booths.