Being a Geezer, 'way back in grade school, an English Grammar teacher hammered into my skull:
One space after commas (,) & semi colons (.
Two spaces after periods (.) & colons ) exclamation marks (!) and interrogation (?) marks.
Periods and two spaces after abbreviations.
Apostrophes in place of missing letters in contractions.
When proofing my posts I was certain I'd entered two spaces after periods ending sentences yet once posting, only one space would appear.
Being a responsible sort'a guy; I'd edit, note two spaces, add one more, save changes and DANG! Still only one space.
In my younger days this would've bothered me; now a days it's just more water of this old duck's back.