There are some dragons that you think you might have hoped to kill off, only to have them come right back rearing at you.
"What is the standard of defending like in the South American leagues?" was a question sent in by one reader this week. "Brazil are infamous for poor defending and only Argentina have true, gritty and hard tackling defenders."
Brazil's Lucio has a reputation as a no-nonsense defender
I suspect that in any list of gritty, hard tackling defenders, Lucio of Brazil and Bayern Munich would be somewhere near the top.
The idea that Brazil cannot defend belongs only to myth. The facts point in the opposite direction.
Brazil and Germany have both played the same number of World Cup games, 91. The difference in their records is not so much in the goals scored (199-192 in Brazil's favour). It is at the other end, where Germany have conceded 113 and Brazil just 84.
Brazil invented the modern back four, and have turned out a conveyor belt of top-class defenders.
A brief glance round the line ups of the Champions League shows that the production line is still working overtime.
But the second part of the same e-mail was much more interesting.
The writer ponders "how easy it is to predict how good a player will become in Europe [after] they have run rings round South American defences, as I believe the standard in Europe is a lot harder, with a greater level of skill and pace required?"
Here the point surely is that the best South American defenders are all abroad, along with the continent's outstanding midfielders and strikers.
It is not the case that the level of defending in South American club football is significantly low - remember how Sao Paulo beat Liverpool and Internacional overcame Barcelona with rearguard actions and the odd counter attack.
One of the most important questions a European club should be asking before signing a young South American player is "can he cope with the speed of our game?
Rather, it is the case that the talent drain lowers the overall standard.
This is one of the reasons that gifted young South Americans on the way up tend to stand out when they are still playing at home, and then frequently go through an awkward period of adaptation when they move to Europe.
The initial shock - which some never get over - is the extra pace of the game.
Recently this was put into figures by Pablo Martin, the physical preparation coach of Argentine club Independiente.
"The big difference that we have with the Europeans," he said, "is that there each player runs between 10 and 12 km per match at a speed of 18 or 19 km per hour. Here we run 8 or 9 at a speed of 16 to 17. It might seem a small difference, but it's not."
The European game is much faster, with less space on the field, more physical contact and frequently much more lenient criteria on how much contact constitutes a foul.
All of this applies even more to the Premier League, well known for being especially frenetic.
So one of the most important questions a European club should be asking before signing a young South American player is "can he cope with the speed of our game?"
If he is a striker, will he be able to withstand the physical battering? Can he cope without picking up the easy fouls he is accustomed to? If he is a creative midfielder, will he able to adjust to having less time to decide what to do with the ball?
If the answer to these questions is yes, then there is a good chance that the ability of the player will shine through.
And then he will prove a major asset to his new team - just as hundreds of South Americans, in all positions on the field, have been fundamental to the rise and success of European club football.
You can put your questions to Tim Vickery every week on the World Football Phone-in on Radio 5 Live's Up All Night programme from 0230 to 0400 GMT every Saturday. You can also download last week's World Football Phone-in Podcast.
YOUR QUESTIONS ANSWERED
Got a question about South American football for Tim Vickery? Email him at email@example.com
Inter Milan's Adriano has recently moved on loan to Sao Paulo in Brazil. Do you think that this move might help get his career back on track?
Here's hoping, and the early signs are good. He scored both his side's goals in a 2-1 win in his first game in midweek - the first one was a terrifying howitzer left-foot strike that brought back memories of him at his best.
I think he's an emblematic case of the forces swirling around today's top players. Body and mind have paid a price for all that money he has earned.
Breaking into the Brazil side meant that he went years without holidays, and the death of his father (who had a bullet lodged in his skull for years - a relic of the violent Rio favela where Adriano grew up) perhaps brought it home to him that he doesn't really have a place in the world.
Though he's not in Rio, he's in Sao Paulo, spending a few months back in his own culture, playing regularly, scoring goals - hopefully it's exactly what he needs. He's not yet 26, there should be much more still to come from him.
Comparing the Brazilian and Argentine leagues, which one is stronger?
Marcus Scharf, Bonn
There's a good way to find out, because the Copa Libertadores, South America's Champions league, gets underway in a couple of weeks.
Boca Juniors of Argentina are the reigning champions, but before that the previous two finals were all Brazilian affairs, and I think my money is on Brazil this time.
Firstly I think Brazilian football has more strength in depth. Argentina produces an incredible quantity of players, but the sheer size of Brazil (its population is four-and-a-half times bigger) means that its easier for Brazilian football to replace the talent that the two countries are constantly selling to Europe.
And at the moment there's another factor - the Brazilian currency is now much stronger than Argentina's, making it easier for Brazilian clubs to bring back players whose move to Europe might not have worked out.
But maybe the form of Argentina's clubs in this year's Libertadores will prove me wrong.
Africa, like its South American counterparts, has always been a force to reckon with when it comes to Fifa competitions like U-17 and U-20 World Cups, and they also do well in the Olympic Soccer tournaments. But strangely, when it comes to the Fifa World Cup, the continent has notoriously failed to perform as well as the South Americans. How have the South Americans transferred the success of their junior teams to their senior side? Is there anything Africa can do to boost the senior sides?
Wurie Bah, Freetown, Sierra Leone
The most important thing, I believe, is the recognition that the youth tournament is not an end in itself, it's part of a process.
There is no point whatsoever in becoming Under-17 Champion if the players are not funnelling through to the senior side.
It's no good - and this clearly applies to English football as well - picking boys who have matured physically prematurely, because this will only give you a short-term advantage.
The success of youth work can only be judged in the long term.
So the youngsters are not just being coaches with an eye on winning the next game, they are getting a course on the identity of their national team - this is vital since the best of them will inevitably spend most of their career in Europe.
Hopefully, after decades of disappointment, these lessons have been absorbed.