The Italian stunned the field to snatch gold in the Covid-delayed Tokyo Olympics, in a European record of 9.80sec.
He made it double gold just days later by helping Italy to victory in the 4x100m relay.
The 29-year-old told reporters he was back at the Summer Games for one reason only: to defend his title in one of its standout events.
"I'm the Olympic champion. I want to win again," Jacobs told reporters.
"I know what I can do. I know I am the Olympic champion. I won the 100m at the Olympic Games. I worked really hard to get here to win again... so I can do the double."
After his stunning success in Tokyo, Jacobs went off the radar, citing fatigue and a knee problem.
We're 'not robots'
His conspicuous absence raised eyebrows and brought criticism that still stings.
"What hurt me was that people didn't understand that we are not robots, we are not machines. We are human," he said.
"We work every day at 100% with our body, so it's normal to have some difficulties, some injury.
"The problem with doping (accusations) after the Olympics didn't touch me because I know what I have to do to get a win, so I know what is not true.
"It's hard to survive at the Olympics and win, but it's harder to continue to win.
"So for that, you have a lot of injury and people didn't understand that.
"In Italy, we never had an Italian guy make the Olympic final, but I won and they continued to criticise me. So it hurt me."
Jacobs showed his determination to bag back-to-back golds by upending his life, both professionally and personally, changing coach in Olympic year and moving, with his family, to the United States to work under Rana Reider.
It seems to have paid off as Jacobs claimed a second European title in Rome in June.
"Of course I've changed since Tokyo," he said. "It was three years ago."
Since then, Jacobs added, "I win, I lose, I have a lot of injury. I change everything. I change country and change coach, so I'm different, but I'm better".
Jacobs maintained that reaching Sunday's 100m final was the hardest part of the jigsaw.
"The most difficult thing is the semi-final because we are this year 15 or 16 guys who can go to the final. The semi-final will be hard," he said.
"Every year is a different, every year there are some people who can run really fast. This year we have the Jamaicans, the Americans, but every year is like that.
"In Tokyo it was like everybody can wait for the silver medal because the gold was being prepared for Trayvon Bromell.
"He ran 9.76sec at the beginning of the season, but he didn't even make the final so you never know. The Olympics are different."
Jacobs concluded: "But it will be fun because there are a lot of guys who can run really fast, but only one can win, and on Sunday we’ll know!"
