By Greg Stobart
The lesson has become ever clearer over the years but Arsenal never seem to learn it; if you are to compete for the highest honours, you cannot keep selling your best players to rival clubs.
Perhaps it all started when Ashley Cole was sold to Chelsea in 2006 after a protracted, ugly transfer saga that eventually saw the left-back move across London.
Maybe it started before then, as far back as the sales of Marc Overmars or Nicolas Anelka - though they were, of course, replaced by Robert Pires and Thierry Henry.
Either way, Arsenal are now a feeder club. One notch below the big boys.
The pattern of behaviour that saw Cole leave Arsenal has continued. The message has constantly been sent out that Arsene Wenger's star men have a price. Roll up, roll up.
Samir Nasri and Gael Clichy are Premier League winners after swapping the Emirates Stadium for Manchester City last summer, while Cesc Fabregas is playing in one of the greatest club sides ever.
The Spaniard will soon be joined at Camp Nou by Alex Song, who is on the verge of a £15 million transfer after a breakthrough in talks between the two clubs.
It is a well trodden path, one taken by Thierry Henry - Arsenal's greatest ever goalscorer - in 2007, Alexander Hleb in 2008, Giovani van Bronkhorst in 2003 and Fabregas last summer.
Sometimes, these players fail to go on to greater things, but the fact is that Arsenal are not at the top table of European football, so those that are feel they can cherry pick the Londoners' best players.
Wenger is a genius in spotting talent and selling players for far more than they cost in the first place, but there are no prizes for having the best bank balance in English football.
Robin van Persie is the latest player to leave the Gunners after backing them into a corner by refusing to sign a new contract.
But what must be really galling for the Arsenal supporters is that he has moved to Manchester United, a direct competitor and a rival in the Premier League.
How can Arsenal ever compete for the title when they sell their best players, key members of the first-team, to the Manchester clubs?
With both Nasri and Van Persie, Arsenal threatened to hold the players to their contracts... but blinked first.
The world knows they are a selling club, and Wenger is constantly forced to deal with the blow of losing players he considered an important part of the club's future.
The squad has been strengthened this summer with the arrivals of Lukas Podolski, Olivier Giroud and Santi Cazorla, only to then take a step back with the departure of the club captain, last season's double player of the year.
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It is a trend, it seems, that Arsenal will struggle to reverse. If, say, Manchester City made a move for Laurent Koscielny next summer, you would fancy that a deal would be done.
Every year Wenger has to prepare for the new season with uncertainty surrounding the future of important players, with sagas that undermine all his work to get the squad ready for the campaign.
You hope that in the future, Arsenal can make a stand and get themselves back towards to top of the food chain. Sadly, that seems unlikely to happen.