According to Bolivia coach Cesar Farias, "playing in the Hernando Siles [the stadium in La Paz] is not like other cities. There's nothing like it."
As Bolivia prepare for their first home game in the new World Cup qualification campaign, Farias is determined that his team should take full advantage from the conditions of their mountain fortress, 3,600 metres above sea level, where unacclimatised opponents are left gasping for breath, and unable to play their normal game.
"We have to avoid the Bolivian lament of being the poor little things," he said. "Let them say that we're nasty, it doesn't matter. But we want to eat the liver of our opponents at altitude."
Argentina are the first opponents with their livers at risk. Bolivia were thrashed 5-0 away to Brazil on Friday, but they can take that with a shrug of the shoulders. They left some of their best players in La Paz, waiting for the Argentines. Bolivia's hopes of making it to the 2022 World Cup are almost exclusively based on picking up maximum points at home. Can Argentina stop them?
La Albiceleste are doing something different. Standard practice at extreme altitude has been for the visitors to climb up the mountain as close to the match as possible, on the afternoon of the game. But Argentina flew to La Paz on Sunday, and will spend two nights at altitude before the game. From a medical point of view, this might be unwise -- the effects of the conditions are thought to be at their strongest after two or three days.
But from a technical and psychological perspective, however, it might be better. Training at altitude helps players have a notion of what they can and cannot do in the conditions, of how they need to adapt their game.
Have Argentina done the right thing? The evidence will emerge on Tuesday afternoon. But whatever the answer, the game will not reveal much about the progress of Lionel Messi and Co. on the road to Qatar. More than anything else, the match is a test of Argentina's preparation to play in La Paz, not their readiness to compete at the end of 2022. As Farias admits, the game in the Hernando Siles is a one off.
Ecuador look to pick up most of their points in Quito. There is no doubt that playing 2,800 metres above sea level can tip the balance. But the conditions are less extreme than in La Paz, and the match will be a genuine test of Uruguay's credentials.
The temporary absence of new Manchester United signing Edinson Cavani robs them of a world class striker, but it also frees them from the necessity to play 4-4-2. With Luis Suarez as a lone centre-forward there is space for a winger, Brian Rodriguez, and for a playmaker -- although Giorgian De Arrascaeta is injured and will miss the match. It also means they can pack central midfield, where they are currently so strong.
But the problem in Thursday's laboured 2-1 win at home to Chile came further back. With Jose Maria Gimenez missing, coach Oscar Washington Tabarez made an unwise choice of Sebastian Coates to partner Diego Godin at centre-back. They are too slow as a pair, and push the team backwards. It will be interesting to see if Ecuador, under new coach Gustavo Alfaro, have the firepower to take advantage.
Another new coach, Venezuela's Jose Peseiro, needs to bounce back after the disappointment of Friday's 3-0 defeat away to Colombia. Peseiro made a poor selection: His 4-2-3-1 left the team too open, and he needs to get the balance right for the visit of Paraguay. Their opponents were the only home team to drop points in the first round. It is not yet clear that coach Eduardo Berizzo is a good fit for Paraguay. An ex-assistant of Leeds United guru Marcelo Bielsa, he favours a bold attacking approach in a country with a footballing tradition of deep defence. A win on Tuesday would do much to consolidate Berizzo's position.
This leaves the two big winners of the first round, both of whom now face stiffer tests.
For all Venezuela's weaknesses, Colombia were impressive on Friday. Coach Carlos Queiroz got his planning right. Juan Guillermo Cuadrado has an interesting double role. He tucks back in as a central midfielder when he must, and appears as a right winger when he can, allowing James Rodriguez to float in from the flank, as he has been doing to such good effect with Everton in the Premier League. And Queiroz made the big choice at centre-forward, leaving Radamel Falcao on the bench and going with the formidable Duvan Zapata. It all clicked on Friday, but will it work as well away to a Chile side who performed better than expected even in 2-1 defeat to Uruguay?
Elsewhere on Friday, Brazil coach Tite appeared to come up with his most coherent response yet to the traumatic Russia 2018 quarterfinal defeat to Belgium. Danilo plays a conservative role at right-back, while Renan Lodi on the other flank has freedom to push forward, allowing Neymar to leave the touchline and cut inside. Meanwhile Douglas Luiz came in as an extra defensive midfielder to sit alongside Casemiro and balance out the side. And Roberto Firmino showed a new interpretation of his centre-forward role, trying to stay upfield rather than dropping deep -- which in Brazil's set up means that he clashes in the same space as Philippe Coutinho.
It all worked in the debut game but Bolivia were almost ludicrously poor. Peru in Lima will be much more difficult. Peruvian morale is high. Their 2-2 draw in Paraguay made them the only away team in the first round to avoid defeat -- and it is precisely the type of game where in the days before coach Ricardo Gareca they would have collapsed and lost. Now, in the first meeting of the campaign between two teams who qualified for Russia, it will be fascinating to see if Peru can carry the fight to Brazil.