If you are over-optimistic, you expect things to turn out better than they really can, or better than the facts make likely. Hope can be wise; this is hope that has stepped past the evidence. A budget can be over-optimistic, a recovery date, a plan for how long the work will take. People use it in calm, slightly careful talk — news, reports, a friend trying to warn you without shouting. It is kinder than calling someone naive, but it still says the bright picture is not well founded. You can use it about a person or about a plan, a forecast, a promise.