A teenager told jurors he planted a bomb on the Tube at Parsons Green as part of a fugitive fantasy fuelled by action films.
Budding photographer Ahmed Hassan dreamed of studying to become the next David Attenborough when he came to Britain from Iraq in 2015.
He told immigration officials he was kidnapped by Islamic State and trained to kill because he thought it would help his asylum claim, he said.
But the Old Bailey heard how he got "bored" and thought about committing suicide in the summer of 2017.
During that time, he got the idea to construct a bomb from homemade TATP after watching films and documentaries, the court heard.
He told jurors: "I think the main reason, I wasn't thinking as a normal person would do. I was very bored, very stressed, very confused and I watched lots of movies, action movies during that time.
"It became kind of a fantasy in my head. I was thinking about it. Yes, that was it.
"I was watching documentaries as well, about fugitives and just the idea of being a fugitive got into my head. And I thought about it and that was it."
Tim Moloney QC, representing Hassan, asked: "Was that an attractive idea?"
He said: "Very much so."
Hassan went about buying the ingredients for TATP and tested 50g of it on a Coca Cola can on the kitchen table of his foster home in Sunbury, Surrey, he said.
He told jurors: "I heard a whoof and a very small heat, fire, for a fraction of a second."
"I was certain that it would not explode. It would just burn.
"I wanted it to look serious so I added the shrapnel to it."
He had stayed awake all night on a sofa in the conservatory ahead of the Parsons Green incident, and his foster father Ron asked why he was not sleeping.
Hassan said he did not answer.
When asked by Mr Moloney where the device was at that point, Hassan answered: "It was next to me."
Asked if he ever intended to hurt anyone, he said: "The idea of killing another human being never crossed my mind at all, never in my life."
Mr Moloney asked if he thought it would explode.
Hassan replied: "Not at all. I was certain that it would burn because I had tested it."
On September 15 last year, the 18-year-old media student planted 400g of TATP and shrapnel on a District Line tube timed to go off when it reached the west London stop.
When he was picked up at the port of Dover the following morning he told police he had made the bomb, which only partially exploded on the packed rush hour service.
Hassan told jurors he wanted to go back to Iraq.
Under cross-examination, Hassan denied planting the bomb to avenge the death of his father, who was killed in an explosion.
Alison Morgan said: "You did feel you had a duty to hate Britain because of the death of your father.
"You believed that coalition forces were responsible for his death. You believed that the fight against Britain should be brought into this country.
He replied: "No, not at all. No, I never thought about that."
Ms Morgan said he was a "proficient liar" and had deceived those closest to him.
He replied: "I never lied. I made up a story for the Home Office to accept me in the country."
Hassan insisted he never tried to blame anyone else, saying: "I left evidence all over the place...I left everything behind to suggest it was me. I actually was seeking them to find out it was me."
Earlier, Hassan told jurors he was never taken prisoner by IS, as he had claimed to Home Office officials in 2016.
Hassan said: "I have never had any contact with Daesh at all."
Asked why he made it up, he said: "Because I came from a wealthy safe area in northern Iraq in Kurdistan and if I told the truth my only reason to leave the country was to further my studies - I felt I had to make up something strong.
"In the Jungle in Calais people used to talk about these things and make up stories. I never came across a refugee who said he would tell the truth when he arrived in the country.
"I wanted to go to university and my ultimate goal was to become a wildlife photographer like David Attenborough."
Hassan told how his mother died when he was young and his taxi driver father was killed
in an explosion in Iraq in 2006.
"So far as I'm aware I was told that he died in an explosion while he was working as a taxi driver. He used to go to work and come back evenings and then he did not come back.
"It was very difficult. I did not understand what was going on. I was in a state of confusion because of fighting, because of bombing."
Hassan moved to northern Iraq with his uncle and older brother and from the age of 12 worked ferrying goods like vegetables across the border with Iran.
The defendant said he decided to leave Iraq because he wanted "a better life".
He smuggled himself to Britain by train and on a lorry at the age of 16, he said.
Hassan told jurors he enjoyed studying photography when he was at Brooklands College in Weybridge.
He said it felt "good to be nominated" when he won student of the year in June 2017, adding he took the same title six years in a row in Iraq.
He has continued his studies while in prison so his "academic year is not wasted", he said.
Hassan has denied attempted murder and using the chemical compound TATP to cause an explosion that was likely to endanger life.