If I'm losing balance in a pose, I stretch higher and God reaches down to steady me. It works every time, and not just in yoga. ~Terri Guillemets 

"Breathe into this."  My yoga instructor always delivers this gentle command at the exact moment when, as my body shakes in an effort not to fall over, I am thinking, "This pose sucks...how long do I have to hold this?"  Every time she says it, I readjust my mind...kinda.  It reminds me to remain in the present moment and feel what I am feeling--good or bad.  And, unlike the advice of the world in your worst moments, it acknowledges that you may be in a tough position at the time and doesn't attempt to change that.  I just end up doing exactly what my instructor says--I breathe into it and accept that although my present condition doesn't feel very ideal (and perhaps yoga ain't for us big-boned chicks), something that flows inside of me will allow me to get through it.  And as I breathe into my pose I can feel my body settle ever so slightly until the next thing I know, I find myself in a different, more comfortable counter pose.