I'll tell you what got me quit...
1. telling myself I was cutting back not quitting. Because I'm the type that if I tell myself I'm not going to smoke, I'll be on the porch chain huffing within 10 secs. I intended to both vape and smoked when I started (I truly didn't believe that vaping was going to work either, nothing else did)
2. Once I started vaping, I vaped 30 mg nic. That's right. 30. I vaped til I felt nic poisoning beginning... MASSIVE headache. Then I told myself I wasn't going to have a cig, and went out back to have a cig... and OMG... GROSS!!! I had enough nic in my system that cigs tasted sooo bad. I started clipping my cig at 1/2... then at 2 drags, then 1 drag... that lasted a while.... the 1 drag and clip.
I say it took me a week, but I was still running out there and taking 1 hit now and then just to see if I was really off it, for about 2 weeks.
When I wanted a smoke, I'd FIRST vape the 30 mg nic til I started feeling a bit sick, then went out for my cig anyway. That conditioned me within 4 days that cigs are GROSS. OMG GROSS. I never told myself I couldn't smoke... but after doing that, I COULDN"T smoke much.
When I got to a point where I believed I could actually stop... I vaped til I had the mother of all headaches and had to go lay down for the 4 hours it took til the nic left my system. Then, did it again when I wanted to smoke.
After that, I was quit. I read that it takes 3 weeks to break a habit... I'd still run out on the porch every 15 minutes or so... and stand around sort of bewildered... LOL! But after 3 weeks, I even stopped needing to run out to the porch.
If you are breaking a decades long habit that was almost impossible to stop, you have to devise a plan that works for you. That's what worked for me. Hopefully you won't have to vape to headache point... but you gotta do what you gotta do. I'm pretty sure you can't OD from VAPING nic, you'll pass out first... I only know that because I did pass out... and frankly, I was prepared to die if it didn't work, that's how bad I wanted to quit, once I realized that it was possible with vaping. Course, I didn't die

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*Edit to say this was a bit exaggerated, I KNEW I wasn't going to die. If you read about nic poisoning, unless you have heart problems, in which case this may not be the best thing to do, the way nicotine kills is it will give you massive headache, nausea, then unconsciousness. It keeps acting, which is why it can kill from ingestion or skin. But once you pass out, you can't vape anymore, so it starts leaving your system. I am NOT recommending you vape til you pass out!!!!!!!!!!!!!!!!!!!!! I am only relating my own experience!!!!!!!!!!!!!!!!!!