For instance, on the Iberian Peninsula in Spain, perhaps the initial smooth sailing of the Spanish campaign made Soult complacent. He even harbored ambitions of crowning himself King in Portugal while the conflict was still unresolved, which caused rifts with several other marshals.
As Soult indulged in the soldiers' cheers of 'King Nicholas,' the Duke of Wellington had already taken command of the British forces on the peninsula, leading his troops to land in Mondego Bay, a hundred miles north of Lisbon.
As for Marshal Soult's performance against the Duke of Wellington, it can be summed up in one sentence: In short, he never won.
However, this can't be considered too shameful, because even Napoleon Emperor himself never won against Wellington.