Why do some words have double consonants while others have only one?

Here are some basic rules for spelling -ing words

Rule 1:Words ending with a Consonant-Vowel-Consonant Pattern

One-syllable words:

ING=If the word ends in a CVC pattern, it gets a double cosonant+ING

Example:

hop>hopping, sit>sitting

Two-syllable words:

ING=If the stress is on the first syllable, the word gets one consonant+ING

Example:

happen>happening, enter>entering

ING=If the stress is on the second syllable, the word gets a double consonant+ING

Example:

begin>beginning, run>running

Rule 2:Words ending in E

ING=If the word ends in E, drop the E,add ING

Example:

donce>dancing, come>coming