The manager of the mine where four men died came out retirement just months before the disaster because he was "bored" of non-working life, a court has heard.
Philip Hill, 44, Charles Breslin, 62, David Powell, 50 and 39-year-old Garry Jenkins died after 650,000 gallons of water flooded the Gleision mine near Pontardawe, south Wales in 2011.
The tragedy unfolded after explosives were used to begin work on improving ventilation inside the mine.
The late quartet's former boss Malcolm Fyfield denies four counts of gross negligence manslaughter - as does pit owner MNS Mining Ltd.
Coal veteran Fyfield said he stepped away from the industry in 2008 because of a lung condition and ongoing back problems.
But the man dubbed "the Alex Ferguson" of the small mining world made a comeback when the owners of Gleision drift mine near Pontardawe, south Wales convinced him to take on the top job.
Father-of-two Fyfield told his trial at Swansea Crown Court his decision to go back to work did not go down well with his family.
But the 58-year-old told a jury coal mining was not just a job, but a way of life for him.
He said: "How did I come back to mining? As simple as it may sound, I was bored.
"Retirement....was life changing.
"It was a change that I did not adapt to very well.
"Did my family want me to go back? No, they did not want me to."
Fyfield's first foray into mining came in 1977 at the age of 23 - and he came from a family of miners with both his father and grandfather working in the industry.
He later went on to purchase and run a number of mines - most notably the Nant Hir and Darrell drift mines.
Fyfield's expertise also saw him head-hunted for other projects.
One of the two specific examples given to the court was The Funnel Project in the Forest of Dean, where a former iron-mine had become home to a rare species of bats.
He also said he took his responsibilities as a mine manager very seriously.
"I have always been extremely careful. I take my responsibilities as a mine manager to a very high standard because of the serious nature of the industry.
"I do not take short cuts. There was no need for me to take short cuts."
Fyfield also gave details about how he had successful submitted two applications in 1992 and 2005 for carrying out work to connecting two mines together - known as a Prevention Against In Rush (Pair) scheme.
The process is designed to make sure dangerous amounts of water, gas or other materials do not flood the adjoining mines.
Fyfield said the reason why Pair applications were needed at the Darrell and Nant Hir mines was because the areas were "non examinable".
He retired from mining in 2008 - largely in part to lung condition pneumoconiosis and a back problem.
However, after having a long break from work his health improved and he decided to return to work.
While at the helm in Gleision, he decided to connect two parts of the mine - H1 and the Old Central Workings - together because of concerns of decreasing oxygen levels.
He insisted he did not need to ask for Pair permission because the two areas were examinable.
Fyfield said he carried out three examinations before giving the go-ahead for explosives to break the coal face away.
However following the firing of the shots at around 9am on September 15, 2011, enough water to fill an Olympic swimming pool burst through the walls.
Fyfield, who had been inside the "stall" area alongside the four deceased, managed to escape after crawling through dirt and sludge in near total darkness.
A jury has been told he now suffers from severe post traumatic stress disorder, sees a psychologist on a weekly basis and takes "high doses" of anti-depressants and anti-anxiety pills as well as sedatives.
He said the horror of the tragedy had totally changed his "life, character and demeanour".
Fyfield also spoke very briefly about his escape from the mine - saying he took on a lot of water and hit his head several times.
He was later placed in a medically induced coma and remained in hospital for two weeks.
At several points during his witness testimony, defending counsel Elwen Evans asked Fyfield if he was okay to carry on.
His evidence has been delivered in one hour blocks, punctuated by regular breaks, amid concerns for his well-being.
The jury has also been told of psychiatrist recommended techniques the defendant may use while in the witness box, such as rubbing his hands together, in order to suppress panic attacks.