Actually in place of vanity you can put just about any sin. Pride, alcohol abuse, pornography addiction, lying, cheating, hating, stealing. Just about everything bad fits in there.
Sin is a symptom.
"To set the mind on the flesh is death, but to set the mind on the Spirit is life and peace." - Romans 8:6
To put your mind on the things of this world brings death, but to put your mind on the things of the Spirit - the heavenly things, brings life and peace.
A rather fascinating sin for me over the years has been vanity in the area of online fame (or something like it). Online fame is really a sad thing to desire, and I'm embarrassed to admit it just about every time I write about it. But what I've realized is there is a difference for me in online activity and online vanity. Activity includes writing for this blog, the sieve and the sand (my other blog), twitter, or other things such as quora. These are not inherently sinful, in fact I do believe (and hope) this blog and my even my mostly blither-full twitter stream might a blessing to some.
But online vanity is something different altogether. Online vanity includes a rather ridiculous amount of time checking the stats for this blog. "Where has my traffic been coming from? How many people have re-tweeted the blither I've recently written? Oooooo, online people I don't know like me."
Yea it's lame.
Well there is an inverse relationship between my online vanity and the quality of my quiet times. When I'm really seeking the Lord, I become caught up in the things of the Spirit, and the things of this world just kind of disappear. It's not even that they all of a sudden seem lame, but more - I just stop thinking about them.
To set my mind on the flesh is to set my mind on sin. Even setting my mind on not sinning is still setting my mind on sin. But setting my mind on the Lord, seriously pursuing Him, makes my sin go away.
And so I've learned my sin is a symptom. A symptom of not seeking the Lord.