Inflation is a result of increased demand with same supply (in worst case. in best case, supply also increases), due to more money on people's hand. As far as I understand it, inflated market is still a market at equilibrium.
For example, say normally a market of bicycles was at equilibrium where 1000 units bought/sold at \$1000/unit. Due to influx of money into people's hand, demand increases to 2000 units but manufactures still can only produce 1000 units. So, manufacturers increase the price to, say, \$1500/unit such that demand again drops down to 1000 units.
In above example, 1000 units are still being sold before and after inflation. Although I understand that inflation does not help, but it does not harm as well (or so I understand). So inflation will lead to new market equilibrium without harming the economy. Why, then, inflation is harmful and central banks need to intervene to rein in the inflation?