I'd say it all comes down to volume. If there's enough money in a currency or in fact any kind of asset it's much less volatile because it's much harder for single players with big pockets to move the needle in either direction.

This isn't really a design issue though (or one specific to cryptocurrencies) but one of making the asset attractive enough in the long term.

Even then larger up and down movements are still possible, for example as seen when George Soros decided to 'break' the Bank of England in 1992.