Benjamin Graham

Quote 1
Investment policy, as it has been developed here, depends in the first place on a choice by the investor of either the defensive (passive) or aggressive (enterprising) role. The aggressive investor must have a considerable knowledge of security values—enough, in fact, to warrant viewing his security operations as equivalent to a business enterprise.
Graham typically referred to passive investing as “defensive”. He believed that most people should choose the passive route because only investing professionals could devote the necessary resources to active or “aggressive” investing:

Quote 2
It follows from this reasoning that the majority of security owners should elect the defensive classification. They do not have the time, or the determination, or the mental equipment to embark upon investing as a quasi-business. They should therefore be satisfied with the excellent return now obtainable from a defensive portfolio (and with even less), and they should stoutly resist the recurrent temptation to increase this return by deviating into other paths.
In Graham’s book, passive investors were better off sticking to straightforward strategies that minimised error:

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