But, when looking a time series, I was a bit confused:

"Actually, fitted values are often not true forecasts because any parameters involved in the forecasting method are estimated using all available observations in the time series, including future observations. When the estimate of involves observations after timet, the fitted values are not true forecasts. On the other hand, naïve or seasonal naïve forecasts do not involve any parameters, and so fitted values are true forecasts in such cases."

When we make a time series forecast, we estimate each point in the future, there is no better fit line as in regression. Then why fitted values are not forecast?

Tank you in advance!