Real estate investing involves the purchase, ownership, management, rental and/or sale of real estate for profit. Improvement of realty property as part of a real estate investment strategy is generally considered to be a sub-specialty of real estate investing called real estate development. Real estate is an asset form with limited liquidity relative to other investments, it is also capital intensive (although capital may be gained through mortgage leverage) and is highly cash flow dependent. If these factors are not well understood and managed by the investor, real estate becomes a risky investment. The primary cause of investment failure for real estate is that the investor goes into negative cash flow for a period of time that is not sustainable, often forcing them to resell the property at a loss or go into insolvency.