If you think you know what will happen in the coming presidential debates, think again. They’re always unpredictable.

The first Kennedy-Nixon debate in 1960 is a good example.

Most pundits expected Richard Nixon to shine. Not only did he have eight years of experience as vice president, he also had a reputation as a skilled debater. But when the camera blinked on, Nixon seemed pale and weak. John F. Kennedy appeared cool, tanned and in command. Nixon’s one-point polling edge before the debate turned into a three-point lead for Kennedy after the debate. JFK went on to win the election by a hair.

In 2000, observers expected Vice President Al Gore, a capable debater, to wipe the floor with Texas Gov. George W. Bush, who was not known for his fluency. But that didn’t happen. In their first showdown, Gore sighed, huffed and puffed, and left a bad impression. His pre-debate lead was wiped out. After all three debates, it was Bush who emerged in first place.

Americans like debates. They offer voters a chance to see candidates side by side. They motivate supporters and serve as tiebreakers for undecided voters.

But the effect of a debate can be temporary. In 2012, Mitt Romney delivered a superb performance in the first debate against President Barack Obama, who was surprisingly flat. Romney erased Obama’s lead and opened a path to victory. But, it didn’t last. Obama’s much improved performances in subsequent debates put the incumbent back on top.

Debates are lost, not won. That was apparent in 1976, when President Gerald Ford intimated that Eastern Europe was not under Soviet domination. It was a big blunder that played into the negative stereotype of Ford as dimwitted. Jimmy Carter didn’t win that debate, Gerald Ford lost it — and with it the election. Self-inflicted injuries are the worst kind.

Debates can make voters more comfortable with candidates, and lessen doubts. Smart combatants use them to identify with the nation’s zeitgeist.

In the closing days of the 1980 election, Ronald Reagan needed to show he had the substance and stability to be president. When viewed on stage alongside President Carter, the former actor and California governor presented the right contrast: strength versus weakness, change versus status quo. He did it by what he said and how he said it.

Debates have big audiences with gigantic media buildups. They work best for candidates who use them to clarify the choice that voters are about to make. They offer valuable opportunities to sharpen messages and sort out issues that have become jumbled in the fog of campaign warfare. That’s why the question Reagan posed at the end of his debate with Carter — “Are you better off than you were four years ago?” — was so effective.

Let’s remember, too, that a candidate’s principal task is not to win the debate, but to win the election.

In 1996, President Clinton was favored for re-election. He needed to make sure the debates did not alter the dynamics of a race that was going his way, even if it meant pulling punches. While his opponent, Sen. Bob Dole, delivered strong performances, Clinton achieved his objective of protecting his lead — and won the race.

Underdogs, however, need to shake things up and take risks. They can do it by unveiling new issues and leveling unexpected attacks.

Looking toward the big event on Monday night — Americans are fixated on whether Hillary Clinton will cough or stumble. If she does neither, she wins round one of the expectations game. If she stands strong throughout all three debates, it could refocus the race in her favor. If she’s put on the defensive, especially on matters that relate to her honesty, she loses.

Of course, viewers will be watching Donald Trump with great anticipation. He’s full of surprises, and in debates, surprise kills. What will he say? How far will he go? He needs to blunt Clinton’s punches, land his own and go toe-to-toe on policy issues. As Reagan did in 1980, Trump must dispel concerns about his ability to be the nation’s leader.

Anything goes in this election. And in the coming debates, anything can happen. The stakes couldn’t be higher.