Why do we drift?

I often wonder why it is that I can be so inconsistent in my spiritual life.  Why do I wander?  Why do I walk away?  I don't want to, and yet I do. And I hate the fact that I do.  I hate that I'm inconsistent, that I'm up-and-down and that I struggle the way I do.  But yet I wander and I drift... and I imagine that you do to (if you are in fact human!).

So, I guess the question is, "Why?"  Why do we wander?  What causes spiritual drift in our life with Christ?

Here's a few quick thoughts that come to mind:

• SIN
  Simply put, Sin = having an affair on God.  Am I cheating God by making decisions that are contrary to His desire for my life with Him?  If I love Jesus, I will make every effort do what he says to do, in everything.  Period.
  

• BUSYNESS
  Busyness is the enemy of intimacy.  Am I so scattered that I feel like I can't create space to connect with God?  Are you? 
  

• LAZINESS & INDIFFERENCE
  Like every relationship, you have to actually want to be with Jesus.  Do I really want Jesus? Like, really, more than anything?? A strong love for Christ does not happen by accident.
  

• LACK OF TRUST
  Do I really believe that Jesus can be trusted with my entire life?  My family, my finances, my relationships, my emotions, my thoughts, my career??  Everything? Or am I gripping onto it refusing to let go? You can't love Jesus without trusting him, completely, with everything.
  

• EARNING MENTALITY
  Sometimes I feel that God owes me.  Like, if I do my devotions and pray everyday, then he owes it to me to be close to me and to be active in my life in tangible ways. How prideful is that?!  That's not grace - that's earning.  We spend time with God because we want to be with him and to learn to love him more completely, not to feel better about ourselves or to manipulate God into doing stuff for us.
  

• LACK OF LOVE
  We love because He first loved us.  I am learning that I cannot love God out of my own resolve & decision...  I can only love God out of response to his incredible love for me.  When I drift, this reality - that God is absolutely crazy about me - is often the first to fade into the background.  But when I'm connected with plugged in with God, when I'm passionate and loving Jesus the best I know how, it's because I am tuned into his incredible love for me.  And I'm just responding to that reality, because I can't help it.
  

There's many more.  What causes "spiritual drift" in your life?