I don't think that's true at all - every organization I've worked with has planned for a 1-2 month ramp-up program. Generally you start off doing trivial bugfixes until the codebase makes sense and move on from there. Hell, learning on the job extends past this phase and is essentially neverending.

You just need to have enough background to make it through the ramp-up phase and start teaching yourself. That holds true whether you went to college or are self-taught.