the candle burns plumb, then does not. the flame leans east; the smoke goes flat and westward across the room. you have not opened a window and the door is closed. and yet.
this means a draft you do not know about. it could be a loose pane upstairs, a chimney swallowing more than its share, or — more interesting — a habit of yours that lets a little of the room out without your noticing: a sentence half-said, a small attention leaking. one of these is the cause.
find the source by sound, not sight. stand still and listen until something hisses, hums, or is unaccountably cold against your ankle. if nothing does, the draft is the habit. mend the habit; the candle will straighten.
— field note: a sideways flame is an instrument, not an oracle. believe what it points at; do not believe what you guess.