Is it worth the struggle?

Feeling like Carrie Bradshaw, I got to thinking is it ever worth is struggling on with a book?

 Nowadays, I only read for pleasure, but I still find myself soldiering on with books I'm not enjoying. There are several reasons for this:-

1. Habit- some of the novels I studied throughout school and uni really didn't interest me, but I had to read them for my course, and I think I'm still under the impression that if I've started something I should finish it. 
2. Recommendations- If the book has won lots of awards or has been lent to me by a friend I feel like maybe they know better and it's worth persevering
3.  Trend- 50 Shades is complete trash- poorly written and problematic, but I read them because I didn't want to be out of the loop. I wanted to know if they were as good/bad as everyone said
4. Needs Must-  I read a lot, and sometimes if I'm away, or haven't managed to get down to the library it's slim pickings and I'll read whatever is available- even if it's not any good
5. Duty- similar to my first point, I feel like I should read some books because their 'classics' and meant to be enriching. However, I've come to the realisation that the classics are heavily dominated by old, dead, white men and their enduring regard is influenced by patriarchal, classist and racist ideas.  

Take my recent library haul- two of these books went straight back. Whit I didn't even open, I read the back again and really didn't fancy it. I attempted A Girl is a Half Formed Thing but the fragmented, experimental style really didn't do anything for me. 

I do wonder if I have perhaps been too hasty however. For example when I started The Knife of Never  Letting Go I couldn't bare it, but have the first 3 or 4 chapters I was hooked. Or at the age of 11 when I was first handed Harry Potter by my teacher I was resistant, as I wrongly assumed that it was about train-spotting. 

On the other hand for some unknown reason I read Martina Cole's Two Women  until the end even though I was completely disgusted by it.  

To make a more informed decision about what is and isn't worth reading I'm going to adopt the 100 page rule. Basically I'm going to continuing reading (even if it's a struggle) and if it hasn't improved, or I'm not enjoying it, I'm going to put the book down and try another. 

What do you think? Have you ever read something to the end and wasted your time? Or, are you glad you stuck with it?