(Concern) After vasectomy

I am deciding to undergo a vasectomy and am currently looking into hospitals. I originally thought that a vasectomy was a procedure that blocks the pathway for sperm to come out, like tying a road. I believed that in some cases it could naturally loosen over time or be reversed later by redoing the procedure. However, I saw on a TV variety show that once you have this done, it cannot be reversed. I had always thought it was reversible, so I am wondering if I was mistaken or if there are different types of vasectomy procedures. If what I believed was incorrect, I feel very conflicted because it might be irreversible.