Examples of factors that cause lower goodput than throughput are: Over Ethernet, files are broken down into individual chunks for transmission.
These chunks are no larger than the maximum transmission unit of IP over Ethernet, or 1500 bytes.
Note that this example doesn't consider additional Ethernet overhead, such as the interframe gap (a minimum of 96 bit times), or collisions (which have a variable impact, depending on the network load).
This example does not consider the overhead of the HTTP protocol itself, which becomes relevant when transferring small files.
The goodput is a ratio between delivered amount of information, and the total delivery time.