The main reasons for constructing a portfolio with multiple assets are primarily to diversify risk and stabilize returns, which is known as asset diversification. Here are the main reasons:

1. Diversifying Risk

Different assets have different characteristics and risk factors.

Even if one asset or market (such as the stock market) declines, other assets (like bonds, commodities, etc.) may offset some of the losses.

For example, when stocks decline, bonds, as a safe-haven asset, typically rise relatively.

2. Stability of Returns

If you rely solely on a single asset, the portfolio may fluctuate significantly due to market volatility.

Including multiple assets can compensate for the losses of one asset with the gains of another, thereby making overall returns more stable.