Analysis
Meet Your New Imaginary German Friend
Imagine that when Kennedy gave the "Ich bin ein Berliner" speech in 1963 there was a sixty-three-year-old German man in the crowd listening to him.
(There were somewhere between 120,000 to 450,000 people in the audience, so one can safely assume that one of them was probably sixty-three and male, but they didn't write down everyone's names and ages so we're going to have to use our imaginations just a little bit.)
Okay, so if this imaginary-yet-entirely-plausible dude is sixty-three in 1963, then he would have been in his teens when World War I started and likely would have had to fight for Germany. This same guy, assuming he lived through that war, would have been in his late thirties when World War II started and might have been called on again to fight for Germany.
Even if he wasn't enlisted, he certainly would have been affected by both wars happening in his country, his city, and maybe even in his house (because war is cruel like that).
So after two devastating wars that same man would have spent the last two decades watching feuding superpowers rip his city in half in a new kind of economic battle. He would have had to deal with the blockade making it difficult to get food and medicine…and all the while his city would have been crawling with four different armies (all of which, by the way, he fought and lost to twice).
Then, as this poor man is entering his elderly years, he gets up one morning to the Soviet soldiers building a wall down the center of town. It cuts through intersections, blocks off the entrances to buildings, and is generally a massive headache. If this old man wants to go visit friends and family living in the East part of town, he has to take his passport and go through one of the official checkpoints where soldiers will frisk him for contraband and may be entirely uncooperative to his needs.
Oh, and people on the East side (possibly our sixty-three-year-old dude's buddies) aren't allowed through the checkpoints at all. They'd be shot and killed if they tried to go over (or under) the wall.
Now Meet Some Real-Life People
The people in the audience at Kennedy's speech had been through a lot. Konrad Adenauer (the chancellor of West Germany who Kennedy mentions as he begins his speech) said, "History is the sum total of all things that could have been avoided" (source).
It's easy to see how Germans—and especially Berliners—would see their own history as a long list of things that they wish they could have avoided. The last six decades hadn't gone very well.
Adenauer spent World War II trying to avoid being captured by the Nazis after they took away his home, job, and all his money. And his story isn't even unique for Germans of this period.
The mayor of Berlin (whom Kennedy praises in his opening line) was Willy Brandt; and no, that's not the name he was born with. He adopted the name when he fled from the Nazis and hid in Sweden. People who had resisted the Nazis and narrowly survived basically governed the whole of West Germany. And now they were on the front lines of the Cold War, too.