The answer may be more complicated than that. Spend hours and hours on the phone with an Apple supervisor to sort out my issues with syncing iTunes on my Mac with my iPhone 6.
Follow these steps sequentially to potential Nirvana: 🙂
1. Go into iTunes on your computer and and click on "View" in the top bar
i. Select "Show duplicate items"
ii. Delete one of every duplicate version (not both!)
2. Exit iTunes
3. Connect your iPhone to your computer, and wait for iTunes to open
4. Click on the iPhone icon (left top with IOS 8)
5. Click on "Summary" under the Setting choices
i. Under "Options" select only "Sync only checked songs and videos" (DEselect all other choices under "Options")
ii. Under "Backups" select "This computer" under "Automatically Back Up"
iii. Under "Backups" click "Back Up Now" under "Manually Back Up and Restore"
iv. Wait for backup to complete.
6. Click on the "Music" icon (below "Summary" and "Apps") and DEselect "Sync Music"
7. Click on "Movies" icon (below "Music") and DEselect "Sync Movies"
8. Click on "TV Shows" (below "Movies") and DEselect "Sync TV Shows"
9. Click on "Podcasts" (below "TV Shows") and DEselect "Sync Podcasts"
10. Click on "Books" (below "Podcasts) and DEselect "Sync Books"
11. Click on "Photos" (below "Books") and DEselect "Sync Photos"
12. Back up iPhone photos to computer
i. Minimize iTunes
ii. Click on Finder on Mac computer
iii. Click on Applications (in Favorites section)
iv. Select Image Capture
v. Cancel scanning software and select iPhone under "Devices"
vi. Select "Import All" photos
vii. Exit Finder when completed
13. Take iPhone and click on Settings" icon (on the iPhone itself, not in iTunes)
i. Select "iCloud"
ii. Turn off "Find My iPhone"
14. Back to iTunes on the Mac
i. Click "Summary" under iPhone "Settings"
ii. Select "Restore iPhone..." under iPhone 6 under iOS 8.1, and wait for restore to complete
iii. Select Restore "iPhone from backup" (NOT as new iPhone!)
iv. Wait for "restore from backup" to complete
15. Select "Music" under iPhone settings in iTunes
i. Select "Sync Music"
ii. Select "selected playlists, artists, albums , and genres"
iii. Select "Include music videos"
iv. Select all "Playlists"
v. Select all "Genres"
16. Now select "Sync" to the right of the coloured and grey bar at the bottom
17. Watch iTunes seamlessly sync with your iPhone after a few minutes.
Why so complicated? Ask Apple! 😉