We all make mistakes, and we all have runs of bad luck every now and then. That stave has short grain across the back, through the handle area. Like the other guys have said putting in a cut out arrow shelf increased the risks of breaking. A shelf if you are going to put one in, goes in at the end of tillering so you can fine tune string alignment, and arrow flight.
That stave was only ready for the start of floor tillering, and not ready for bracing. If a bow breaks at the handle, and not in the limbs it means that the limbs were not bending enough(by a long long way). Having said that if you got the limbs moving first and didn't cut the arrow pass, that stave probably would have given you a decent bow unless the grain was crossing like that in the working area of the limbs.
This may sound harsh to you, but unless you want to throw away money lay off the yew for a while, get the basics down right, with cheaper more available staves. Patience is one of the most important factors in the early stages of bowmaking, coax the stave into a bow. Speed and the apparent devil may care attitude come once you get plenty of experience. Don't despair, I'm sure it won't be long before you are ready to tackle and do some justice to a nice piece of yew.
I've broken plenty of staves myself in the early days, usually poor selection of grain in board staves or backings, despite patience and careful work.
Hamish.
