They say Half knowledge is Worse than having No knowledge ?Is it true?

Yes! It's true. Even my lecturers used to say that "half knowledge is very dangerous."

I think that half knowledge can be dangerous in some situations especially in situations where you don't realize that you have half knowledge. In that kind of situations the person thinks that they will be able to do the same things as a person with full knowledge. That can lead to some dangerous situations for instance if you think that you think that you can fly a plane, and just decide to try it despite the lack of full knowledge (because you overrate your own skills) There are also other situations where half knowledge is problematic for instance in situations where people think that they have understood something and start teaching other people those things without realizing that they haven't understood everything properly.

For those who pretend to know it all, it's true because they are using their half wit to manipulate or degrade other people.

Surely, it depends which half! I'd rather go to a doctor who knows half the subject than one who knows none of it - at least there's a 50-50 chance he might get it right. On the other hand, a scientist who rejects the God of the Bible (scientists don't even know half of all the science there is to know) is on to a loser.

yup, having half knowledge is really worse than having no knowledge, because they can't manage that, it is like staying in the middle of river while crossing,,, having good knowledge is who already crossed the river and having no knowledge is who didn't start crossing the river, having half knowledge is the person in the middle of river and don't know how to continue,,,, it is really really worse because I have faced these type of situations before...

It depends according to condition. For Example, You knows something about flying a plane, but not everything. And if for some reason if you fly a plane, than there is heavy chance of meeting accident. Also, if you have a little idea of creating a software, but you create one and hopefully sold it, it might not work properly,and you get very bad reviews. people will angry at you. And you knows a little about how to write a Blog, and so if you start writing, you can easily get more ideas how to write. No one can knows everything, that's why there is different professions for different people. have a good day