The third class of evils comprise those which everyone causes to himself by his own action. This is the largest class, and is far more numerous than the second class. It is especially of these evils that all men complain, - only few men are found that do not sin against themselves by this kind of evil. ...This class of evil originates in man's vices, such as excessive desire for eating, drinking, and love; indulgence in these things in undue measure, or in improper manner, or partaking of bad food. This course brings diseases and afflictions upon the body and soul alike.
MaimonidesOne should see the world, and see himself as a scale with an equal balance of good and evil. When he does one good deed the scale is tipped to the good - he and the world is saved. When he does one evil deed the scale is tipped to the bad - he and the world is destroyed.
MaimonidesIt should not be believed that all beings exist for the sake of the existence of man. On the contrary, all the other beings too have been intended for their own sakes and not for the sake of anything else.
Maimonides