Employee gets fired on the spot after giving their 2-week notice, boss then calls them later begging them to come back and finish out their notice period: 'I gave 2 weeks' notice. They fired me on the spot, then begged me to finish the week'

Giving two weeks ' notice when you work in a jurisdiction that has "at will" employment is always a risky move. They can fire you on the spot without cause anyway, so why are you giving them a cause? Doing so is merely a good-faith gesture and a sign of trust and respect, and possibly a desire for a continued relationship with an employer who has shown you the same over the course of your employment and relationship with them. Of course, people can surprise you in the worst of ways, so it's always best to consider this carefully.

A lot of reactionary and egotistical managers and business owners will take your intention to depart them as a slight and won't take kindly to their loss of control over you, so when you give them forwarning that you're planning on leaving anyways they'll exicese the last little bit of control they have over the situation and end things on their terms, and in their mind saving the cost of paying you for the next few weeks. This, of course, is very short-sighted. The thing is, two weeks' notice exists solely to pass on legacy knowledge of your position and to provide continuity and train a replacement.