Doubt about "I wish"

Dear all,

I was told that when "I wish" is used, no matter what, what the writter wishes would not be true.

For instance:
I wish you would allow me to present it tomorrow.

By using "I wish" in here, according to what I was told, it indicates that I will definitely not be allowed to present it tomorrow.

I was told that if we want something to happen in the future, without denying the possibility of it, we should rather apply "I hope" instead.

For instance:
I hope you would allow me to present it tomorrow.

By using "I hope" in here, it indicates that there is a chance for you to allow me to present it tomorrow, and I desire the probability to be true ultimately.

All right, so there is a problem now, I really doubt about what I was told, what I have leanrt. Does "wish" this word really do implies that what the writer desire must going to be unture?

I wish you would kill him <- Can this implies that the probability for you to kill him is low but it could still be true, or this must be unture?

What about I hope, ah... I am thoroughly confused now, please clearify these two words and their usage for me. Hope and Wish... thanks , thank you very much.