Each investor must decide for himself or herself what is an acceptable level of potential volatility for a preferred level of return. Under conditions such as currently prevail, Benjamin Graham, in The Intelligent Investor, would likely have recommended no more than a 25% investment in stocks or stock mutual funds, with most of the balance in cash, short- to medium-term bond assets, or real estate.
A similarly prudent approach to real estate investing at this time might call for no more than 25% of one's income from all sources being paid out in mortgage, taxes, insurance, or other fees directly related to real estate ownership. If the outlay is presently more, then the suggestion would be to either increase income or sell real assets until the 25% threshold is not exceeded.
But I understand that for individuals who are very familiar and comfortable with the prospects and risks involved in an asset class, such as equities or real estate, a higher than recommended percentage of one's net worth might be maintained in the category in question. In a few cases, there might even be a market situation that is as close to a sure thing as possible, and then it would be foolish to dump an asset just to assure some rigid and conservative allocation guidelines are met.
With commodities, particularly precious metals, even if they are held as a hedge against inflation or setbacks in other markets (for example, precious metals often do well in times of financial uncertainty, when there are fears of unpleasant things: severe political disruptions, big losses from a natural disaster, a substantial rise in the price of oil, possible war with another country, the potential for new acts of terrorism, etc.), the usual recommendation is that they not be more than about 5-10% of one's total holdings, since they are so volatile themselves and often do not offer much investment value other than to offset losses in other categories.
I personally am not comfortable with options or with selling stocks short, but some find such measures to be worthwhile types of speculation when stocks are fairly high. But there is always the possibility stocks will go much higher still. I have heard that investment money manager and columnist Ken Fisher thinks US stocks will go up a very significant percentage this year. Perhaps he has a crystal ball.