Traffic graph LAN vs. WAN newbie question

[pnwbob]

When I'm downloading a file it shows the bandwidth in the traffic graph as WAN (in). That makes some sense to me, but it also shows as LAN (out). This is a bit confusing to me. I guess the file is leaving the LAN when it goes to the computer? The opposite is true during upload where the bandwidth appears as LAN (in) and then WAN (out).
The WAN side seems intuitive, but the LAN side isn't. A diagram would help the most.

[maverick_slo]

You are correct.
Imagine it like lan is uploading to your pc, so traffic is leaving iface…

[jahonix]

What's coming in on WAN cannot come in on LAN as well. It has to leave the unit, doesn't it?
If traffic enters on both interfaces then you have a NAS.