@RiverBlossom, what usually causes actions to cancel automatically is when there is something blocking the sim’s ability to get to whatever task you have given him/her. It usually means that you have to trace the path between your sim and the location of the task and remove any obstacles in the way.
...and believe me, it can be a royal pain to figure out. That is one of the reasons why I keep my sims’ houses so spartan. It’s not because they’re averse to buying stuff. It’s because half the time they’re too ~brain-dead~ to get from point A to point B without getting stuck somewhere. :mrgreen: