Mistake and Certainty

Wittgenstein speaks a lot about a mistake in his notes about Certainty. May be the German to English translation is not so good, if took sometime for me to see what is ment by it.

2+2=4 is a rule, you cannot prove it.We are taught that it is correct. Wittgenstein speaks about "war would be a mistake here like?" We find 2+2=4 is always true and never wrong. It is difficult to understand, what is this mistake all about. This example will show it: 2+2=5, well it is wrong, but how do you know it is wrong? If it's a rule we can't prove it, also we can't disprove it. Here is how mistake will come, say we give this formula as correct to a math student to remember. Say he don't know whether it is true or false. He will try it in real life. Here finds each time when he appalys this rule a mistake is made.  He adds two apples to another two apples he should get 5 as per rule but in reality he gets 4. This is the mistake referred by Wittgenstein. When we think wrong rules as correct we get mistakes.

World is made up with rules like 2+2=4, not only mathematical but also physical, like length and time. These rules cannot be proved. It is a build up in the human brain, from birth onwards. So qualities like space and time are made up by us. These cannot be said to be made up 100% by our brains. Suppose we want some quality that we want but don't physically exist, we can't create it in the mind and feel those qualities. So there is a fine difference. We cannot create qualities, but the qualities that exist are created by us. These qualities have a consensus among everyone. So, is it correct to say some quality that don't exist if everyone except, it becomes real? Another thing is you should not forget this"everyone" should include nonhuman entities - observers.