What is the meaning of 'the end does not justify it'?

First answer (not true):

"The end does not justify the means" means that what ever effort or what ever reason you had for doing some thing was not was not justified, because the end result was not what you wanted. And so all of the time and effort to reach that end was wasted.

True answer:

"The end justifies the means" is a phrase which means that, if you have a goal, it does not matter how you reach it, as long as you reach it. For example, say that your goal is to get an A on a test. If you believe that the end justifies the means, cheating on the test to get the A does not matter to you. All that matters is that you got the A.

"The end DOES NOT justify the means" is a phrase meaning that you must take a moral route to reach your goal. You cannot break the rules or do anything bad in order to reach your goal. If you wish to get an A on a test and you believe that the end DOES NOT justify the means, you would probably study or use legitimate means to get the A on the test.