What's the difference between compulsion and habit/regulation?

I've seen constantly that a compulsion is ANY action taken to neutralize the fear, but considering I have bpd as well I require emotional regulation through things like mantras or radical acceptance, aka small actions done to reduce emotion. My brain will point to that and essentially say that I cannot do those things because that would be doing a compulsion which we're not allowed to do. Typically it would be easy to assure a fear away, and this isn't me asking for reassurance of my own obsession, more so asking the technical difference between the two concepts since I can't find a clear answer anywhere.