Sincerity isn't enough.
I found this out the hard way early on in marriage. Just weeks after our wedding, Lisa had her twentieth birthday. I was a new husband then, completely unintiated in the finer arts of marital conversation, so when Lisa said, "Don't worry, my birthday's no big deal," I made a terrible mistake.
I believed her.
What else could I do? My campus pastor had told me, "Go for the godly ones." so I had. Lisa was, indeed, one of the godliest women I had met in college. The only problem was, my college pastor never warned me that godly women can occasionally lie.
Caveat to guys
I was reading in the book I'm almost done with, Sacred Marriage by Gary Thomas, and came across this quote that other girls in my suite found amusing but true: