So offcoarse some years will be less than 10% or perhaps slightly negative, but on average 10% is achieveable.
Long term returns of 10% pa are impossible, unless: (a) you have an uncanny knack of buying the best investment properties, (b) credit is infinitely accessible, or (c) the income of home buyers grows at a similar pace.
Constant 10% gains across the entire market would cause mortgage repayments to exceed the median income within 20 years, which is clearly not going to happen.