Entirely depends. Once I realize it's long I look back at the title, and if it's mildly interesting and the title seems worth it i keep going. Otherwise scroll down to the end of it, and then it depends on how much I have left.

If it's picture, I will look at the whole thing
If it's words, is like probably just go pass it really fast then read the comment
If the comments are interesting
Then I'd give it a chance