What science does, in fact, is to select the simplest formula that will fit the facts. But this, quite obviously, is merely a methodological precept, not a law of nature. If the simplest formula ceases, after a time, to be applicable, the simplest formula that remains applicable is selected.
-- Russell, B. (1953). On the notion of cause, with applications to the free-will problem. In H. Feigl & M. Brodbeck (Eds.), Readings in the philosophy of science (pp. 387-407). New York: Appleton-Century-Crofts.
In other words, UseTheSimplestFormulaThatFitsTheFacts?
The pain arises, of course, during that period between the time the simplest formula ceases to be applicable and the time the simplest remaining formula is applied. -- anonymous
And, sometimes the old, simpler formula is still useful. Dealing with "ordinary" scales of size, mass and time, Newton is still great stuff. I don't need to take relativity into account when I'm moving at a tiny fraction of C.
This is very much related to TheStructureOfScientificRevolutions.
On the other hand, YouArentGonnaNeedIt
See also OccamsRazor