As polls get set to close in Israel with Prime Minister Benjamin Netanyahu facing a tight reelection battle, keep in mind that Israeli exit polls are just as unreliable as American ones.

Voting stations will close at 3 p.m. Eastern time, and the early exits are expected to drip out around then. But it won't be until much later that we get a sense of how the actual vote turned out, and if things were close, it will take days or longer to figure out the next prime minister.

In 2015, polls predicted Netanyahu was a goner, and then, early exits showed his Likud party more or less tied with the liberal Zionist Union party. But in the end, it turned out that Netanyahu enjoyed a significant victory, with Likud winning 30 seats to 24 for the Zionist Union.

The unreliability of polls is a function both of the complex parliamentary system in Israel as well as the tendency of Likud voters to be more reluctant to participate in polls.

To become prime minister, an Israeli politician has to be able to put together a coalition that adds up to a majority of 61 seats in the parliament, or Knesset. So what everybody is waiting to see tonight is not just how well the two top parties did (this time, it will be Likud and the centrist Blue and White), but ultimately whether the right-wing bloc or left-win bloc ended up with more support collectively.

Further complicating matters is that for a party to get any seats, it has to meet the threshold of winning at least four. Anything below that amount and those votes essentially get discounted, and the seats get apportioned among the parties that did meet the threshold. There are 39 parties running this time around, of which 14 are expected to make it into the Knesset. Given how the parties on the bubble can have a big impact depending on whether they get just above the threshold or below the threshold, it's difficult to tell where things will end up until the votes have been counted. At that point, the horse trading begins to woo the smaller parties into a coalition, which could take days or even weeks.