[exim] Confused about SEEN in filter

why does this work?

if $h_From: contains "mperkel"
then
seen finish
endif


but this doesn't

if $h_From: contains "mperkel"
then
seen
endif

It seems to me that if a message is considered "seen" then it should be
diiscarded. But in the second case it is ignored. The reason I'm doing
just seen is bacause I'm doing other thigs after the seen.