Entia non sunt multiplicanda praeter necessitatum.* - William of Ockham
Numquam ponenda est pluralitas sine necessitate.** - Same guy
If a thing can be done adequately by means of one, it is superfluous to do it by means of several; for we observe that nature does not employ two instruments where one suffices.*** - Thomas Aquinas
Simplicity is the ultimate sophistication. - Leonardo da Vinci
Brevity is the soul of wit. - William Shakespeare
It seems that perfection is reached not when there is nothing left to add, but when there is nothing left to take away. - Antoine de Saint Exupery
We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances. - Isaac Newton
The supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience. - Albert Einstein
The simplest explanation is almost always, "Somebody screwed up." - Dr Gregory House
No need so complicating one lah. - Mr Tan, my 4th Form Maths teacher
Ah, the wonderful irony of this list...
I must say, though, on purely aesthetic grounds, I think Shakespeare's the winner here. Also, my opinion of Thomas Aquinas has dropped drastically.
* Entities should not be multiplied beyond necessity.
** Pluralities ought not to be posited without necessity.
*** WARNING! WARNING! BULLSHIT DETECTED!