Much of it has been found in confronting parts of a hostile host community in Scotland who could not quite work out, nor offer up a reasonable argument why they detested the man from Lurgan so much. Apart from the fact he existed and managed to prosper in their midst.
"How dare he.." was the great unsaid from the great unwashed when listening to some of Lennon's bulging, wild-eyed detractors.
Most of the incessant attacks on Lennon came about because he was a high-profile Northern Irish Roman Catholic running Celtic, and one who was not prepared to kowtow to those living in the dark ages.
The death threats, the bombs in the post, the assaults in the street and the ongoing vitriol were passed off because he had ginger hair, was a bit in your face and was generally a bit narky. This was Lennon's real-time experience at Celtic without the 3D glasses.
Against such a backdrop, what would combustible 'Cork boy' Roy Keane have discovered in Glasgow apart from similar small-mindedness, and possibly worse? Probably a similar level of anti-Irish racism that Lennon unearthed.
Keane had intimated to Ireland's former Celtic winger Aiden McGeady that he would have lived in Edinburgh if the Celtic job became a viable prospect. Like he had done when he spent six months at Celtic in the death throes of his career in 2005/2006.
Thankfully, the prospect of Keano succeeding his former team-mate eight years after he played alongside Lennon at Celtic Park is off the agenda.
There were more than a few onlookers who were quite relieved when the news broke yesterday that the former Manchester United captain Keane had decided against becoming Celtic manager. There were quite a few more who were happy. Mostly because he is not the type of coach who is required at Celtic.
His name may have flogged a few thousand extra season tickets, but come the bleak mid-winter in Scotland, he would have discovered the same truth that troubled Lennon so much in recent times: Celtic are a hard sell to their own supporters because there is no competition.
As hard as this may sound to some, a league without a challenge from Rangers - or some other club - is not good for business. Celtic may boast well over 40,000 season ticket holders, but a lot of supporters are not sure about participating in a Scottish Premiership that concludes before Christmas. One lunchtime match with Hearts in December felt like it could have been housed at the club's Lennoxtown training ground.
Despite the obvious shortcomings of the landscape, Keane does not have a managerial record that befits the stature of a club as protruding as Celtic. Yet it seems the Irish owner Dermot Desmond was preparing to forego all that knowing that Keane would enhance sales of season tickets. And also knowing that Keane could not fail to clasp the league trophy at the end of his first season.
Celtic are a selling club, but the descent of traditional rivals Rangers into liquidation and rebirth in the Scottish Third Division in 2012 has forced Celtic to continue to cut their cloth to suit their needs.
They look to find talent, nurture it and sell it on. It has been very successful in seeing the club clamber into profit, but they don't need Roy Keane to oversee such a philosophy.
They require a coach to encourage younger talent to prosper, not one who has yet to prove he could succeed under such a business model. The former West Bromwich Albion manager Steve Clarke, the latest favourite for the job, sounds a much brighter fit - if less sexy than Keane, who has had some troubling times in management. His last posting as a manager with Ipswich lasted 20 months, and saw him win only 28 out of 81 games.
The mortality rate of Celtic managers is around four years if they are not sacked. Martin O'Neill lasted five years, Gordon Strachan four years and Lennon four years. Tony Mowbray was sacked in under a season after losing sight of his surroundings, but that was when Rangers remained a clear and present danger.
Ireland coach O'Neill was probably surprised Keane opted against Celtic, but he arrived in Glasgow when Celtic possessed Henrik Larsson and were selling Mark Viduka to Leeds United for £6m and buying Chris Sutton from Chelsea for a similar amount. Times have changed in the 14 years since O'Neill first picked a Celtic side.
Keane perhaps showed a greater awareness of what he could have walked in at Celtic by deciding that the job was not for him. Not without a cheque book. Not when your remit is to coach, rather than buy.
He was not seduced by the name of the club he supported as a boy in Cork. Lennon showed similar sure-footedness by departing at the right time.
Celtic are too strong for Scottish football, but financially weak in Europe. The ceiling of their ambition is reaching the Champions League. With three qualifying rounds to be negotiated as early as next month and downsizing apparently continuing to take effect, there is a decent chance they will not be there for a third straight season.
Lennon's success at Celtic in claiming three straight titles and reaching the Champions League last 16 is unlikely to be bettered in the near future. Not unless some investment is found to find a higher calibre of recruit. Keane probably knew this after some introspection.
What does Keane's decision to stay as Ireland's assistant coach, and until earlier on Tuesday his job as an ITV pundit, tell us about the state of Celtic that we did not already know?
It tells us that they may be a 'global' club with the European Cup to their name, but that finance does not match the size of the support. If Lennon was prepared to depart his 'dream job' without another one to go to, it says enough.
Celtic cannot ask people to stump up money for season books without knowing what they are buying, who they are going to be watching or having faith in a manager who is convinced by the job description.
Victor Wanyama was sold to Southampton for around £12 million and Gary Hooper went to Norwich for £5m last summer as Lennon was faced with his stomach-churning yearly rebuilding project.
When the Greek forward Georgios Samaras announced last month that he had not discussed a new contract with the club despite wanting to stay, Lennon probably felt that his work there was done.
There is nothing to be gained by hanging on when you've lost faith.
There comes a time in every man's life when he has to move on for the sake of himself. Ambition and hope are two of the greatest things a man can possess. Without them, all is lost.
Perhaps the most admirable quality Neil Lennon displayed during his four years in Scotland was not winning titles, but having the foresight to walk away when the time was right. In having the self-awareness to realise that his time had come and gone.
- Sports & Recreation
- Neil Lennon
- Roy Keane