The Africans went down 1-0 to Mexico on Friday, Oribe Peralta scoring the only goal of the game.
The tight nature of the result did not reflect the game, however, Giovani dos Santos saw two goals harshly chalked off for offside and Cameroon rarely offered an attacking threat.
Eto'o and his team-mates face Croatia next in Group A, needing a win to keep their hopes of progression alive with tournament hosts Brazil to come.
And the veteran is keen to see his colleagues remain confident when they tackle the Croatians.
"It's important for us to remain positive. We wanted to start the competition with a positive result, but God wanted it otherwise," said Eto'o.
"We can beat any team on our day, but we'll have to be at our best to beat Croatia. It won't be easy because they're in the same position as us.
"Now, we have to turn our attention to preparing as best we can.
"We absolutely have to beat Croatia to have any chance (of staying in the competition). We lost to Mexico, but that doesn’t mean it's all over."
