Adrian Douglas of Market Force Analysis writes that in his experience, most ordinaly people have difficulty understanding why gold is the investment opportunity of a life time. Blaming the messenger, he explains it in simple terms, making a distinction between consumables and collectables:

gold and silver are highly prized collectables that are selling like ordinary consumables at just above their cost of production. Through market manipulation and interference their scarcity premiums have been annihilated through surreptitious supply that can not be maintained. Just like consumables their prices can not go meaningfully lower because no one produces real things at below cost for long. There is a near certainty that they will regain their collectable
status soon and acquire massive scarcity premiums in line with their true supply and demand fundamentals as demand increases and central banks stop selling gold, and even start buying it instead.

In the last paragraph, he addresses the fear of investors, who dread that precious metals’ heyday might be over:

Some investors may be concerned that perhaps they have missed the bull market in precious metals because gold has risen from $255/oz to $1000/oz while silver has risen from $4/oz to a high of 21/oz. This rise in the metals only reflects the increased costs of extraction. There is no scarcity premium included. No bull market will ever finish before very large scarcity premiums have developed. Investors have missed almost nothing. The major gains are still ahead.

http://www.marketforceanalysis.com/index_assets/WHY%20OWN%20PHYSICAL%20GOLD%20and%20SILVER%20.pdf