It happens. Improper wedging is sometimes worse than no wedging at all. A wedge will only do so much and when you get to the point where you're stacking wedges you're asking a lot. I've done it and I'll undoubtably do it again but it's usually because I read a tree wrong and I'm trying to make up for it.
Too much lift will sometimes break a hinge before you're ready for it. When that happens you've lost every bit of control over the tree and gravity takes over. Run.
If you're all sawed up in the back cut and you're wedged up tight and nothing is moving just wait a minute and see if anything happens. See if the tree is rocking on the wedges. Sometimes it's hard to see but any little bit of wind will make a difference.
You can keep trimming your hinge down but beyond a certain point...and that point differs with every tree...you're gambling.
All this talk about the hinge being set at a certain percentage of the tree's diameter and if you do this the tree will always do that is absolute crap... pure and simple. If every tree was exactly the same maybe making hard and fast rules would work. Our job would sure be easier if things worked that way.
One way that I've found to start moving a tree that stalls out is to trim a little...very little... off the hinge on one side to where you then have a tapered hinge. Wedge it but don't hammer the wedge tight. I don't usually agree with wedging anywhere but in the desired direction of fall but in this case it usuallly works to get the tree started. Usually. Watch your wind. Just be ready to run because with that piece of the hinge gone, the rest of the hinge tapered, and your original wedges driven tight that tree will go where it wants to.
Hey, every once in awhile one goes sideways on you. Once in awhile you'll cross the lead. It shouldn't happen very often though. Makes the skidder operator grumpy.