Let me pose a hypothetical situation to you.
There is a class of History students. They all take a test and the students who worked hard get As. Those who did nothing and sat around all day got Us.
The teacher suggests that the next test will be different: the average grade of the class will be the grade that everyone gets.
So the students take a test. The students who work hard get As again and those who did nothing get Us. There are some students who did a little work so they get a C perhaps. The average grade is found to be a D, so everyone gets a D.
The hard-working students are annoyed and realise that there is no incentive for them to do any work at all as they will be dragged down by the people who no work at all. The same is true for the somewhat working students. The students who did nothing are happy as they did nothing yet got a higher a grade as they were helped by those who did work hard.
A final test is taken and all the students get Us, so the average grade is a U. The students now all have the same grade and everyone is equal.
This is why Socialism can never work and why Jeremy Corbyn's wage policies will never work.