Change........no one likes it. It is everyone's dream to achieve a level of longevity during their career, usually in one place. While this is sometimes possible, it is a rare occasion in this day and age of radio.
Sometimes, change is for the best. What are reasons to consider a change? Perhaps you have maxed out on advancement opportunities within the organization you currently work for. Perhaps a conflict of personality exists. Perhaps change is a part of your 5-10 year plan. Whatever the case, do not be afraid to embark on a new venture. Take what you have learned from all of your experiences to date and make the next experience something that others will talk about.
Lastly, when exiting your current organization, make sure that you show them exactly how grateful you are for the experience you are taking away. This is done by thanking people in person, email communication, acknowledgement of these superiors in the press release that announces your new position, amongst others. This works in your favor, as your previous employer sees that you are thankful for the experience that you received, while the new employer sees that you are humble.
Change can be difficult, but it is ok. Don't ever be afraid to go get what you feel you deserve.