Every Lions tour and every Lions squad is unique, and will evolve and create its own spirit in an incredibly short period of time. There will be no voting, just a lot of discussion about the attributes the coaches feel each player can bring, but ultimately it is the head coach who has to be happy.
That said, there are certain rules of thumb, certain criteria, which I would always apply when trying to select a squad...
1. Pick players on form
I cannot stress this enough. There simply is not the time available to pick players who are not on form and allow them to "play themselves in". It is also vital that the players themselves know you are not selecting on reputation.
2. Pick players who have consistently performed well under pressure
This is where Wales' players have possibly let themselves down a bit over the past eight months or so. Their form under pressure has just not been good enough.
Scotland, too, while they have had a really encouraging time since the World Cup, their defeats by France and particularly England were massive setbacks, when the spotlight was really on them.
Players such as the Gray brothers and possibly Finn Russell would have fallen down the pecking order there, I would imagine.
By contrast, Ireland's players - guys such as Robbie Henshaw and Garry Ringrose, Jonathan Sexton and Sean O'Brien - delivered when it mattered. Their autumn form and their finish to the Six Nations will have helped their cause.
3. Pick players who are quick to learn and assimilate ideas
With such a short build-up, it is imperative that players can take on board new ideas and put them into practice in double-quick time. There is such a short window to assimilate the coach's game plan, so you need rugby intelligence, as well as talent to tour with the Lions.
I believe it is the collective rugby intelligence, which will be so important and necessary to beat New Zealand.
4. Pick players who understand "collective intelligence"
It is not just about learning and adapting your own role. It is about understanding how to implement the game plan in a team context, developing a game that can challenge the All Blacks.
Talent is one thing, but the ability to share knowledge from different perspectives to make the greatest and most significant impact lifts the team performance to a different level.
This is where the Lions of 2009 and 2013 got it right.
5. Pick players with the right character to create the right Lions identity
The big difference between the Lions and any other team in the world is that each Lions squad is a reflection of that specific group of players. It is not like a nation, which has its own identity, regardless of which players are selected.
Each Lions squad is unique. Players must be big enough to take on the challenge of moulding that identity, putting their stamp on it.
I see someone such as Owen Farrell and I think he can take on that responsibility.
6. Pick dynamic players
There has been a lot of talk about the physical side of the game, almost an assumption that the Lions will need to outmuscle New Zealand ... to beat them up, to blast them off the pitch.
It is a cliché of northern hemisphere rugby v southern hemisphere rugby. Of course, the Lions will need to be physical, but I believe it is a dynamic, evolving game that will most challenge the All Blacks and put them off their stride.
They are hugely physical themselves and will be ready for that confrontation, so we must have speed into positions, into shape, into contact, in our decision-making.
We will have to be incredibly accurate, and capable in a few weeks. It requires every player to see and adapt to opportunities and threats.
That is the team dynamic, which the Lions will want to have in place leading into the first test.
7. Pick role models
You need role models in any squad and particularly so in a Lions squad, where guys from different countries, who may not know each other, are coming together for such a short time.
I would put Sam Warburton, Rob Kearney, Jamie Heaslip and Alun Wyn Jones into this bracket. And Jamie Roberts.
He has to be in contention for me, despite losing his Wales spot over the autumn. Big man and a big leader.
With those criteria in mind, I then sat down and mapped out my Lions squad. I ended up with 46 names, 25 who are the essential core and 21 from whom the final critical 12 will come.
So I will leave that as my long list, but one thing I do know - it will not be easy for Gats.
That last selection meeting is never easy. As a Lions coach, it is wonderful to be able to tell players they are going, but devastating to leave them out.
That responsibility weighs heavily on your shoulders.
McGeechan's Lions longlist
Back three
Stuart Hogg, Liam Williams, Elliot Daly, George North, Anthony Watson, Tommy Seymour, Jack Nowell, Leigh Halfpenny and Rob Kearney
A mixture of experience and new talent is needed in any Lions squad, which is why I think guys like Kearney and Halfpenny must be in the frame. Halfpenny's goalkicking is also a serious weapon.
Against that, you weigh the other criteria mentioned above. I think Gats will go for seven or eight of these nine.
Centres
Jonathan Davies, Robbie Henshaw, Garry Ringrose, Jamie Roberts and Owen Farrell
A mix of experience and in-form talent, so important in the positions between back row and back three.
Fly-halves
Jonathan Sexton, Dan Biggar
Farrell, of course, can play 10 or 12, which means I have only picked two other fly-halves, but I think there will be serious discussion about Finn Russell, my wild card. This is a player I sense could grow with the challenge and support of the Lions environment.
Scrum-halves
Ben Youngs, Danny Care, Rhys Webb, Conor Murray
I think Gats will go for three of these four. The one he will leave out will depend on the game plan he is decides to go with, and who he picks at fly-half.
Looseheads
Mako Vunipola, Joe Marler, Jack McGrath, Cian Healy
Again, it is three from four. Ball-carrying in this group could be an important asset and influence the final call.
Tightheads
Tadhg Furlong, Dan Cole, Samson Lee
Hookers
Rory Best, Dylan Hartley, Ken Owens, Jamie George
Which three hookers will Gats take? Big decisions here.
Throwing in is the key, as well as ball-carrying. The final choices could come down to the "chemistry" element.
Second row
Alun Wyn Jones, Maro Itoje, George Kruis, Iain Henderson, Courtney Lawes, Joe Launchbury, Richie Gray
I see this as the most competitive area in the Lions squad and also the key to beating New Zealand, whose partnership of Brodie Retallick and Sam Whitelock is fearsome.
Whoever Warren goes with will have to match them, blow for blow. I think he will take five of these seven.
Back row
Sam Warburton, Billy Vunipola, Ross Moriarty, Taulupe Faletau, C J Stander, Peter O'Mahony, Jamie Heaslip, Sean O'Brien, Justin Tipuric
It is eight from nine here and I would not want to be in Warren's shoes. You can make a case for any or all of them.
This area is an exciting part for the Lions, it is trying to judge the effect of the combinations of players who will be coming together for the first time and could produce devastating rugby.
