There are many teams that perform well against strong teams and perform poorly against less strong teams. Sometimes strong teams do not know the past analysis of weak teams and their players in detail so during training, the match situation goes against them due to not knowing the strengths of the opposing team players. If they were aware of other strong teams and their players in advance and practices their strategies to counter them in advance it would be easier to play against them. The same situation was seen in the case of Barcelona, they performed poorly against Rayo Vallecano. But despite being a weak team played very well because the Vallecano players were aware of Barca strengths and went to the field after studying the players of the opposing team.
Strong club realize their opponents are weak, so they field second-string players without realizing that the weaker clubs have made changes in their game plan and also different players when entering a new season, so the strong clubs conclude they are still weak. Well, this is what often causes surprises when seeing strong clubs play weak clubs, meaning they have underestimated from the start without thinking the weaker club will make it difficult for them.
This is a lesson for strong clubs that they really need to pay attention to changes that occur in weak clubs to avoid making mistakes that can prevent them from getting full points.
Exactly. Most of the time strong clubs field second string players against weak teams or rest their best players. That opportunity is used by the weak team players to attack the strong team and defeat them. But in the Barcelona and Vallecano match Barcelona second string team was not there. They took the field to face their opponents with the best players in the match. It is really surprising that clubs often do not learn from previous analyses. They soon realize the consequences of underestimating weak teams.