Why does scp get stalled? How do I resolve it?

Sometimes when attempting to copy a file ( of size x ) over the network using scp, you may get an error like the following:

filename stalled

or it may just sit there and display:

--:-- ETA

This usually happens because scp is trying to grab as much bandwidth as possible, and a delay in grabbing this bandwidth (say on a busy network or by firewall rules, etc.) can stall it. In this situation, limiting the bandwidth (with -l option) will fix it.

(Please note that the -l flag takes it's size in Mb, not MB).