I'll reference Alessandro Barbero, his episode on the italian retreat at the end of WWI.

Basically he said that the Italian govt didn't want to enter the war because they knew how fucked up the army was. They saw how poorly it performed in Ethiopia and didn't fancy their chance against European Nations.

However the people didn't know that, it was all covered up. And there was sens of connection between the italian people and France. That was particularly the case with educated italians, Barbero noted, which are influential in journals and the "good" society. The liberal democracies, France and UK, embodied well their values and ideals for which they wished Italy to fight. They wouldn't let liberal values fall. So the pressure mounted little by little, journals after journals, discussion in posh café after discussion until the govt had to ceide to the pressure.

It didn't make a mistake joining as much as it pretended to be stronger than what it was to its people.