If you decide to make the financial investment to start college, it makes sense to finish. That does not mean it necessarily makes sense to start in the first place.
That investment is a sunk cost. It definitely may make sense to finish, but throwing more money after your initial sunk cost shouldn't be why.
This is not really true: once you have spent your money, it may stop being sensible to go on with the 'thing': buying a ticket for something in the future. You have spent the money but you are under no obligation to 'perform' it. If it sucks, you had better lose your money and not waste your time than both.