Before the Industrial Revolution – when men, women and even children flocked to the factories to make a living – it was far more common for workers to travel from job to job.
Rather than joining a team, tradesmen, craftsmen and labourers would move around on their own, carrying their own tools and supplies, and find work where they could get it.
The easiest way to lug their tools around was in a sack, which they would then leave with their employer for safe keeping. The origin of the phrase, therefore, starts to become clear.
With no job security, contracts or trade unions, workers could be discharged at a moment’s notice.
Once their services were no longer required, they were literally given their sack, before being ordered to pack it up and leave.