NOTE/caveat emptor: I “stole” (borrowed?) the original passage below as well as the two punctuated "takes" on it from the book "The Complete Idiot’s Guide to Creative Writing." I swapped the names and genders only (in my version, John becomes Mary and vice versa); it doesn’t change the point of the exercise at all, though.
So, imagine you find this letter stuck within the pages of a library book you are reading:
Dear Mary
I want a woman who knows what love is all about you are generous kind thoughtful people who are not like you admit to being useless and inferior you have ruined me for other women I yearn for you I have no feelings whatsoever when we're apart I can forever be happy will you let me be yours
John
How would you read it? It contains no punctuation; specifically, no commas, periods, dashes, or question marks. Thus, the meaning must be guessed at.
There are two valid ways to interpret it, which are diametrically opposed to each other in meaning and tone. Adding punctuation after different words makes all the difference. Czech it out (if you are not from the Czech Republic, simply check it out):
Exhibit A:
Dear Mary,
I want a woman who knows what love is all about. You are generous, kind, thoughtful. People who are not like you admit to being useless and inferior. You have ruined me for other women. I yearn for you. I have no feelings whatsoever when we're apart. I can forever be happy—will you let me be yours?
John
Exhibit B:
Dear Mary,
I want a woman who knows what love is. All about you are generous, kind, thoughtful people, who are not like you. Admit to being useless and inferior. You have ruined me. For other women, I yearn. For you, I have no feelings whatsoever. When we're apart, I can forever be happy. Will you let me be?
Yours,
John
Note that in the original version, the spelling of the words is correct and unambiguous. It is only the punctuation that is missing, but that is enough to leave the meaning completely open to interpretation and imagination.
The moral of the story is that if you want people to understand your writings, use punctuation in the appropriate places.