Hierarchy of principles / Golden Rules

In Maths the children are taught the BODMAS / PEMDAS ...Brackets Of divisions, Multiplication, Additions & Subtraction or Parenthesis Multiplication, Division, Additions & Subtraction. These are simple rules to apply to complex long maths sums. ( notice the simple rule is that the multiply / divide has to be done before adding or subtracting!)

Like in English we have some rules like 

"I becomes before E, except after C" or "P is silent when before an S" and few more

Similarly in Chemistry while handling chemicals there are rules.

Rules have been made after years of study, research & evaluation as the simplest, smartest, safest & sure shot method of doing something.