Back in the 1980's I wrote two horror novels (on Wordstar
). Self-publishing back then was only through vanity presses - and quite expensive. After sending a ton of query letters out an agent took me on - accepting my first, then later my second book. Anyone who has gone this route knows that getting an agent's attention is FAR from the end of the game... my agent would send teasers (the first 30 pages) out to publishing houses every month: no interest, not right for us, etc. I was paying my agent $60 every month to send the queries to the publishers. After something over a year, I gave it up and trunked the books.
There was no internet to investigate agents, or even do research on how to get a book published back then. (Only the ARPNET was around - I was on it, but it wasn't much use). As Sage and Lizmonster suggested above, I eventually reached my limit and decided to pull the plug.
After I retired and began writing again I went straight to self-publishing.