"Insert mode" not working

Hi!

This issue has bothered me for a long time and it's the main reason why I've never really been able to get into Premiere. Every time I try to edit a video the issue ends up bothering me enough for me to switch to another editing software.

Well, the issue is the command shortcut – it simply doesn't work, ever. All I want to do is move/insert a clip between two other clips while pushing (all) the footage forward, making a "hole" for the footage I'm inserting. Should be simple enough, and whenever I hold down command key (I'm on Mac) and drag a clip the rightfacing arrows do appear, but when I place the clip it still overwrites and deletes sections of the clip to the right. It's so frustrating and I can't for the life of me figure out what's wrong. 

Any help would be greatly appreciated. I'm working on a project with a deadline right now and unless I solve this quickly I'll have to edit it in another software...