Conflict--why is it so hard??

Spent this past weekend with the Olympia RWA Chapter at Manresa Castle in Port Townsend with some of the most fabulous people on the planet.  Had a wonderful time, and took up the current MFH (manuscript from hell) to work on.  Writing it has just turned into such a struggle.  And I discovered with their help that the reason is. . . . there's no conflict.  The hero and heroine both wanted, basically, the same thing. 

This makes for a very short book.

In my head, they had opposite goals, but once people with a clearer vision looked at my plot (or lack thereof), they said, "Hey! There's no conflict here, and no place for your characters to grow."

On the flip side, I think I helped a couple of people with the same problem with their manuscripts. 

So why is it so easy to see these ginormous plot holes in other peoples' books and not in our own?  Is it because we're too close to the characters?  Is it because we don't spend enough time before sitting down to write to get this figured out?  Or do we not go deep enough?  I mean, this is something like book #7.  I should have this figured out by now.  And I **thought** they were at odds.  But they're really not. 

I have a whole notebook full of 'deep insights' into this book that clearly meant squat.  I'm going to start fresh because I still like the characters, but I was heading them in the completely wrong direction. 

So today's question is, How do you ensure you have enough conflict?  How do you recognize when there's not enough?  And where do you draw the line between revising what you've got, and throwing it out and starting all over? 

Adrianne Lee told me that you need Goal, and Opposition to that goal.  And that both of those should either be heroic, or someone doing something unheroic, but for a very good reason, a heroic reason.  Part of my problem was that my heroine wanted freedom and/or self-determination, which is heroic, but the OPPOSITE of that, which would have to be the hero's goal, would be to deny her her freedom.  Bad juju there, at least for a hero.  One of the many reasons the book wasn't working. 

In my bullfighter book, the heroine wants to kill the story's villain.  Now, murder is generally not considered heroic, BUT she's going to avenge the murder of her family by the villain years earlier.  And of course, the villain does die in the end, but not at her hand, so she's still left being heroine-like.  Heroic.  Whatever. 

Thoughts?  How do we test our conflicts to ensure they'll be sustainable for an entire book?