Santos, whose side need to beat Hungary on Wednesday to qualify without depending on the intricacies of the best third-place rule, added that his team's performance in the 0-0 draw with Austria was one of the best of the tournament.
"I'm staying until July 11th and I'm not going to be on holiday," he told reporters on Tuesday. "How can I make this promise? Because I believe in my players. Why shouldn't I believe in them?
"Why is it that, suddenly, we have gone from being optimistic to pessimistic?" he said. "Portugal gave one of the best performances of this tournament and, afterwards, it seemed we had done nothing.
"I have a fantastic group, with attitude, determination, total effort and quality. It wouldn't make sense not to believe in them."
Santos said he rated Portugal's performance in the 1-1 draw against Iceland as "reasonable to good" and against Austria as "good."
"The only weak point was that we didn't convert the numerous scoring chances we had. There's no magic wand, I can't pull rabbits out of a hat, but I believe that if we continue like this we can convert some of them (against Hungary)."
Santos repeated the declaration he made on Sunday that Cristiano Ronaldo would continue to take penalties and free kicks, despite his penalty miss against Austria and generally wayward shooting.
"They said before the tournament that Cristiano was smiling too much. Now they say he is not smiling enough," said Santos.
"But he will get over this and do what he does best, and what he has proved he can do all his life, which is to score goals."
(Writing by Brian Homewood in Nice; Editing by Ian Chadband)
