Not only far from inevitable but impossible in a lot of cases. When I was looking for an apartment in Germany most (all? I can't remember) landlords wanted to verify that my income was at least three times the rent.
I wrote “as much as.” So this varies from town to village, and how much income you have. So of course for some rich people it will be 10%, but I would guess for most its ~50% (living quality / income trade-off), while you really want it to be below 15% for a decent flat.