It is a very important concept based on the Going Concern Concept. We book the value of assets on the cost basis, not on the net realizable value or market value of the assets based on the assumption that a business unit is a going concern. No doubt, we reduce the value of assets providing depreciation to assets, but we ignore the market value of the assets.
The cost concept stops any kind of manipulation while taking into account the net realizable value or the market value. On the downside, this concept ignores the effect of inflation in the market, which can sometimes be very steep. Still, the cost concept is widely and universally accepted on the basis of which we do the accounting of a business unit.