Not everyone decides to go to film school, obviously. There are a number of perfectly good reasons for that too; the cost, the relocation, the relatively low chance an employer will ask for it.
But deciding not to go to film school doesn't mean you don't have to work hard, practice, and solicit feedback on your work - whatever the department you want to work in.
In his recent article An Alternative Film School For Editors, editor Jonny Elwyn Jonny outlines the costs of a year long DIY editor education. He includes a downloadable spreadsheet of what to buy, and a list of website resources to use for learning theory, and places to get hands on editing practice.