what is the example of grand theories?

The GUT or TOE "Theory of Everything" is the unification of Relativistic and Quantum Physics, probably via String Theory.

One of the common theory's is that the Colorado River carved the Grand Canyon, yet this is not a fact. There are other theory's how the Grand Canyon was formed. One Theory suggests that there was three great lakes in Arizona, Utah, New Mexico and partly in Colorado. The Kiabab Uplift created a natural dam. The Kiabab Uplift eventually breached and formed the Grand Canyon in a matter of a short time.

Both theory's have holes in them.

Difficult things are difficult to do.

Big Bang