How Do You Know When It's Time?

I talk with people all the time who for one reason or another want out of their current job, but can't seem to make the move.  They know they should, they know their not happy and that they're being held back from their potential.  But the comforts of the routine (even though they hate it) hold them like glue.  I remember the day I finally made the move.  I had pushed to envelope so many times that I had to move or risk being let go.  As I look back I still can't figure what made it feel so hard.  I think it really boils down to not having enough confidence in myself.  Even though I knew I could do it, something kept telling me I would fail.  Only when failure seemed a risk at both ends was I able to make the jump.  A jump I now look back on with pride.  I hope those of you who are considering a move will weigh the options both seen and unseen and then believe in yourself and take the leap that will transcend your life into a new realm.  Go for It!