[gentoo-user] triggered by backtracking - what does that mean?

[Helmut Jarausch]

Hi,
would anybody please explain what the following means:
emerge -vp net-libs/libpcap
Calculating dependencies   * waiting for lock on  
/var/db/.pkg.portage_lockfile ...                 [ ok ]
... done!
[ebuild   R    ] net-libs/libpcap-1.5.3  USE="bluetooth dbus ipv6  
-canusb -netlink -static-libs" 0 KiB

Total: 1 package (1 reinstall), Size of downloads: 0 KiB

!!! The following update(s) have been skipped due to unsatisfied  
dependencies
!!! triggered by backtracking:

net-libs/libpcap:0


Many thanks,
Helmut