But not every use of the passive is wrong. First, let's be clear what the passive voice is.
The noun that would be the object of an active sentence (such as, Our troops defeated the enemy) appears as the subject of a sentence with passive voice (e.g., The enemy was defeated by our troops).Why it is a weak construction can be seen in its use by politicans. "Mistakes were made" doesn't tell us who made them, which is the point of saying it that way.
However, we should use the passive voice on certain occasions. Here are some.
- The actor is unknown:
The cave paintings of Lascaux were made in the Upper Old Stone Age. [We don't know who made them.]
- The actor is irrelevant:
An experimental solar power plant will be built in the Australian desert. [We are not interested in who is building it.]
- You are talking about a general truth:
Rules are made to be broken. [By whomever, whenever.]
- You want to emphasize the person or thing acted on. For example, it may be your main topic:
Insulin was first discovered in 1921 by researchers at the University of Toronto. It is still the only treatment available for diabetes.