Project management by definition involves temporary endeavour with the goal of creating something new. It has a beginning, an end, and an objective that can be achieved. As a result, it is often (not always) temporary group of people, the project manager often does not have HR responsibilities, and there is a limited horizon. The emphasis is on one-time result. Think building a new high rise building. General management is repeatable process: there is no end date and the process is often "business as usual". General manager manages a fixed group of people that repeats the same task day in and day out. Think a maintenance crew that cleans and maintains the aforementioned building after it is built.
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