That is certainly true here in the USA. If you think about it, it is also fair.
The part of the 800 € you pay on the mortgage, the principal, is capitol (an asset) that didn't just disappear. When you sell the property you'll get it back, minus the mortgage interested and expenses, plus the rent and any appreciation of the property's value.
What you're talking about is negative cash flow. That's okay as long as you have other income to offset it. Then, if you invested wisely, you'll make a profit when you sell, and you will have used Other People's Money (OPM) to make a bigger profit than if you had paid cash for the property and had no mortgage at all.