Joe Biden’s irritation was evident.

During his interview with ABC’s George Stephanopoulos, the president almost seemed to shake his head in disbelief throughout.

If his thoughts had been revealed in a word balloon above his head, they would have read something like this:

“My opponent kept falling asleep in the courtroom where he was being tried and ultimately convicted on 34 felony counts, mistakenly identified a photo of a woman who had accused him of sexual assault in a civil case as being one of his ex-wives, forgets when he’s speaking on the stump who he’s running against and who’s president now, tells a lie with every other breath—and I’m the guy you’re asking to prove his fitness to hold office?”

Biden’s implied argument through the Stephanopoulos interview was that he’s being held to a different and higher standard than Donald Trump is. The president thinks he’s being treated unfairly.

Biden is right, but his contention is beside the point.

More on that in a moment.

I understand Joe Biden’s frustration.

The place where I was born—in a housing project in Cleveland, Ohio—isn’t far removed culturally or geographically from the president’s birthplace in Scranton, Pennsylvania.

I have a good idea of the waves of condescension Biden had to wade through as he started his climb. I can guess how many self-styled blue bloods sneered at him because he didn’t go to the right schools or come to the office with a social pedigree.

What sustained him while he made his way in the world was the same quality that does so for every American striver—a determination to endure and keep moving forward. He learned that lesson young and it has carried him through the tragedies of losing his first wife and two of his children, along with the lesser disappointments of political defeats and other setbacks.

You can hear that bedrock determination in the Biden refrain repeated again and again following his disastrous debate against Trump: “When you get knocked down, you get back up.”

A core Biden belief is that things happen in life that are beyond our control, but how we respond to those events is entirely our responsibility.

As I listened to the Stephanopoulos interview, I was struck by how often Biden said his failure during the debate was his fault and his alone, but when he started to tout his accomplishments as president and was using the first-person singular—the word “I”—he quickly caught himself. He said the victories were possible because he has a great team with him.

The contrast with Trump—who can’t stand to share credit with anyone and blames every setback on someone else—was stark.

Biden said once he wouldn’t even be seeking re-election if Trump weren’t running again. While that likely isn’t true—the engine of ambition driving a lifelong striver like Biden never rests and always finds fuel—it explains at least part of the president’s unyielding refusal to step aside.

Guys like Joe Biden learn young that the last guy you let back you down is a trust fund baby such as Donald Trump, a career scammer who’s spent his entire life ducking the consequences of his misdeeds and fleecing the people you grew up with.

When a guy like that tells you he wants a fight, you give him one.

You keep getting back up no matter how often you get knocked down.

You don’t quit.