For me the hardest day certainly wasn’t the day I quit or even the day after that. Most people would except that the day you quit cigarettes for good would be the hardest day.
For me I think it’s about the 2nd or 3rd day of quitting or stopping that’s actually the hardest.
It’s partially due to the nicotine flushing out of your body, it’s still around after a couple of days so the cravings get more and more intense.
Remember drink a lot of water, this will help you flush the nicotine out of your body. There are some more tips in How to Quit or Stop Smoking Cold Turkey.
The day you quit is not so bad, because you can take not smoking for 6-8 hours without feeling too bad anway (think of a long haul aircraft flight, they are ALL non-smoking now).
The day after you quit is reasonable too, you get some bad cravings, but for me it wasn’t THAT terrible..
It was worse after that during the 2nd and 3rd days, man those day for me were REALLY tough.
Just remember, be prepared for it and you’ll be fine, know your triggers, get support and be ready for the hard days, it might be different for you, depending on how heavily you smoked, the rate your body flushes out the nicotine and so on.
Don’t fall into the trap of thinking the first 1-2 days will be the toughest though, as you might fall down when it gets harder.