This precept breaks down into two points of common sense:
2-1: "Do not take harmful drugs."
2-2: "Do not take alcohol to excess."
This is, of course, common sense. One who is on drugs does not always see the real world in front of them. They can be dangerous as they are not really there. If one was working with a person on drugs, or driving on the highway next to them, there is a possibility of that person doing unpredictable and often dangerous things.
When one takes alcohol to excess, they are not alert. Alcohol impairs one's ability to react - even when it seems to the person drinking that they are more alert.
Both drugs and alcohol have cause innumerable pain and hardships on those around the drug or alcohol user, as well as to the user themselves. These scourges have caused countless deaths, the majority of deaths caused when they are used to excess.
"Observing from the points above, one becomes more physically able to enjoy life."
*Temperate: Not going to extremes; not overdoing things; controlling one's cravings.