I emptied the trash, I was doing some clean up work of all the stuff I don't need and accidentally put the folder in there. and most of my folders in the library are empty too, is the Startup Items folder important?
also, I'm starting to face another issue. Whenever I start up my Macbook, a window appears saying that that the items in the "Startup Items" folder could not be run because of some security settings. I've looked in about how to fix it but seeing how the Startup Items folder is deleted, I'm not sure how to