[ZenoArrow]

To give an example of something a smart investor would do, Warren Buffett supposedly only invests in industries he understands in depth:

http://www.investopedia.com/articles/05/012705.asp

What proportion of investors would you suggest show such restraint? Over half?

[lmm]

The proportion of "investors"? Low. The proportion of market capital allocation, among people doing active allocation for long-term buy and hold strategies? Very high.