Complex sentence: Investors who do not want to do this (those who buy into indexes or securities that use indexes as their basis) are called "passive" investors-they link their portfolios to the broad market and do not try to out-guess conventional market wisdom.
Split into simpler sentences: Investors who do not want to do this (those who buy into indexes or securities that use indexes as their basis) are called "passive" investors. They are known to link their portfolios to the broad market and to not try to outguess conventional market wisdom.