Switching jobs is sometimes similar to switching shoes.
The old shoe, no matter how expensive, wears off after a few years and after that it only slows one down. It only gives sores, blisters and pains and no longer meets your needs, goals and expectation. A crappy shoe shows its true color months (sometimes only weeks) after you discard your old shoe and change into this one.
No shoe is no blessing either. During the initial adjustment period, you only regret and have remorse which makes one long for the old shoe which we had so carelessly left by the dumpster. Some people even manage to retrieve the old shoe and beg for it to be your best buddy again. However once the initial adjustment period is over, more often then not, one finds the new shoe to be a better fit for your toe. This time the only thing you would be thinking was, why the hell did I wait so long to try this one out. However by the time you are 100% sure that you and your shoe are fit for each other, the shoe starts fraying.
On a serious note:
Employees ofter overestimate their capabilities when they threaten to quit, but one should always remember that the corporation will continue to exist (and hopefully flourish) long after you have parted ways… much in the same way that you will continue to grow and flourish even after you have severed your ties with the current job. The job never defines a person, its just a stepping stone preparing you for bigger and better things (both professionally and personally)