People keep telling me that if the timing belt on my 4Runner breaks it will seize the engine, if this is true could someone explain the mechanics of it? Why would it do that? Either way please cite your source, THNX!

The timing belt runs the overhead cam shaft that opens and closes the valves. If the belt brakes a valve may be all the way open when the piston comes up. When this happens the piston will slam into the open valve then it goes down hill from there. Check out howstuffworks.com