You can smoke a cigarette in different ways. You can smoke half of it and throw it away, or smoke it until the end, until you feel the smell of burning cigarette filter.
The stub can be off in an ashtray, or you might throw it on the ground and let it turn off by own, or by pressure of people's feet, or tire of a car or something else.
And some people are used to smoke it up to end, then throw it on the ground, while crush it under their shoes until the cigarette paper's ripped and the shattered filter skips out.