For people who were experiencing a "bad day" yesterday. Life goes on without smoking and life will have its good days and bad days. Quitting smoking helps insure you will overall have more days, and because of better health you will be able to more fully enjoy the good days and even be better equipped mentally and physically to handle the bad days too.
Bad situations (death, illness, relationship problems, work troubles or job losses, bad economic times, etc.) will still occur and make for down times. But time helps all of us assimilate even the most tragic of circumstances and we bounce back to carry on with our lives. Even after the death of those closest to us, over time we can get back to happy and fulfilling lives.
Time does not improve smoking though. Smoking gets worse and worse over time, and your health deteriorates more and more over time. The kind of damage smoking can induce does not always lend itself to just bad days or bad moments in a day--it can lead to pain and discomfort that continues till death ends the chronic suffering.
Again, while it may sound cliché and flippant, any day you overcome every obstacle smoke free was a good day in that one respect. That one respect helped to extend your health and save your life. Take satisfaction in your accomplishment for that day. To feel the same satisfaction everyday, remember what a good job you did staying smoke free yesterday and vow today to recommit to never take another puff!