Yesterday was the painful reminder of the biggest and toughest of all, the 36th anniversary of the horrific car accident that left him without the use of his legs.
It was also the day the 60 year-old millionaire businessman broke cover to fight for his own credibility in the wake of Craig Whyte's shambolic purchase of Rangers that has left the football club in administration and clinging on to its very existence.
In his plush office in Edinburgh's Charlotte Square, there was no attempt to sugar-coat the situation as Sir David spoke for the first time about why he sold to the shamed Whyte. There was an instant apology, genuine regret and a hope that Rangers can survive.
As he surveys the wreckage of a club he owned and ran for 23 years – at times recklessly – Sir David insisted he did everything he could to carry out background checks on Whyte, who bought the club from him for £1 last May before embarking on a nine-month period of stewardship that has taken the SPL champions to the brink.
Sir David produced damning documentation on Whyte as his trusted lieutenant, Murray Group finance director Mike McGill, clearly and concisely outlined his boss's part in proceedings.
Letters received from Whyte's London-based lawyer Gary Withey, of Collyer Bristow – one unsigned and dated October 11, 2011, and an identical copy signed and dated on January 3, 2012 – insist Whyte and his team had lived up to the terms of the takeover.
The letters insist £7.8 million, pledged in the official Share Purchase Agreement outlining how Whyte would buy Rangers, remained in Whyte's Collyer Bristow client account. But last week Rangers' administrators Duff & Phelps seized just £3.6m from that very account, leaving £4.2m unaccounted for.
Sir David told The Herald: "The letter on January 3 is quite dynamite because what they've done is confirm they would deliver the deal they signed up to. That has never been in the public domain.
"As early as August, there was a sort of 'wait a minute, this doesn't seem to be quite right' from us. You've now got that for the first time. It does not look good for Craig Whyte at all."
Sir David was asked why he sold Rangers to Whyte. He said: "It's ironic you should meet me today. It's 36 years today since I had my accident, March 13.
"I'm not trying to be some tough or arrogant person, but I've had quite a few obstacles put in my life. I have a responsibility to accept that I sold the club to the wrong person.
"If I could turn the clock back, of course I would. There's not much more I can say than that.
"I deeply regret selling the club to Craig Whyte. And if the information had been available to me at the time I wouldn't have done it. I did it in good faith.
"There's only so much information. After someone has been disqualified for seven years (as a director), it's not that easy to check. And it is also down to the individual, is it not, to make us aware of that?
"So we did check, to the best of our ability. But I was in a situation where we had been endeavouring to sell the club for four years. We had received proof of funds. We had a legal document confirming he was going to spend money on players, eventually, once he had paid back the loan."
Sir David added: "I'm not defending myself because I've made a huge mistake here. He met the criteria that were in his offer document. What we wanted to do was get debt out the club.
"I thought: 'I hope I've done the job right. I've passed it on. This is a guy saying he's going to spend money on players, on health and safety, do the ground up. That is a legal offer document. You would expect that to be honoured."
Two major questions have gnawed at everyone since Whyte's short-term reign began to unravel, culminating in the club going into administration on February 14.
Firstly, just how did he manage to mortgage off more than 100,000 advance season ticket sales, raising a sum of £24.4m, of which £18m was used to repay the club's debt to Lloyds Bank, a full month before he completed the takeover of Rangers on May 6?
Whyte's entire transaction remains at the centre of a police investigation. So far, nothing has been decided as to whether any wrongdoing took place.
There has been an allegation made already that "financial assistance" may have taken place. That is when a company's assets are used to buy that company over, which is against the law.
Sir David said of the season ticket deal: "The first I knew about Ticketus was when Martin Bain (Rangers' former chief executive) asked me to do a precognition on his defence against Craig Whyte, and it was brought to my attention at the end of December.
"I signed a precognition in January with our lawyers, Gateleys, and Levy McRae (Bain's lawyers) present, and that is there to go into the court.
"We had never heard of Ticketus before (that is, Ticketus involvement in the Whyte deal as the club had used them previously for short-term finance deals), and for people to think we knew earlier – there was nothing at all. How did he do it? That's a good question."
The second major question concerns Lloyds Bank. It had been running Rangers with an iron fist for almost three years. Debt had been driven down to the £18m mark from £35m.
With a potential tax liability centred on Rangers' use of Employment Benefit Trusts, was it not the case the bank was desperate to get Rangers off its books? Sir David insisted the bank did not pressure him into doing a deal with Whyte.
"No," the former owner said. "The bank wanted their money back, of course, and I'd made it clear I wanted out of Rangers. We were going into recession and people weren't queueing up to buy football clubs.
"Lloyds wanted out the football industry. I wanted out the football industry. But if we'd known of the Ticketus thing, we'd not have done the deal."
Sir David said he has spoken to Whyte a few times since the chaos began to ensue. He also revealed Whyte had rejected advice on how to approach life as Rangers' owner.
He said: "The day I met him, he asked me for advice. I said do not become chairman for a year and ensure you keep Martin Bain on to see if you can work together. You'll need him. And for his own reasons he decided to dismiss Martin.
"The day of administration I phoned him at 8.30am. I got a text saying 'I'm busy, I'll phone you later'. And I've not heard anything."