Frank Herbert broke into the SF field with “Looking for Something?”,  published in Startling Stories in 1952.  Prior to that he’d been a newspaper writer and was good enough at fiction to have a story published in Esquire in 1945.  The online bibliography is thin, there are references to a couple of other non-genre stories in between, and that he also published under pseudonyms, but no evidence is given of what those anonymous stories were.  Like many writers of that era, he may have adapted an unsold story into SF to give that market a try, and meeting with success found that someone with his talents could get published as an SF writer more easily than as a conventional fiction writer.  This must have also aligned with his own interests in the inner workings of the mind, the meaning of consciousness, and environmental issues.

This first SF sale is a story within a story.  The inner, longer one concerns a hypnotist who during a routine performance of his ability develops the notion that there are certain recesses of people’s minds that are blocked to them, as though by an external force.  He works with a woman to try to unlock these hidden “instructions”, but they are so deeply embedded that she believes she’ll die if she even articulates them.  The framing story involves an alien bureaucracy whose job is to harvest something called “korad”,  a source of immortality, from humans and use it for their own society.  They worry that the hypnotist came dangerously close to discovering their mind control, and take steps both to have him given another profession, and to review their own procedures to keep this from happening again.

Herbert touches on a few ideas here with questioning what is the true reality, and whether our minds can hold secrets unbeknown to us, all very topical for the time in which this was written (PKD published his first stories in 1952 also), but somewhat tacked on to make this story into SF rather than just a psychological study of hypnotism.  Startling Stories had faded from its past glories by this point, but their diminished reputation also allowed them to publish less conventional SF.  Herbert is probably the last significant author to break into the field with this magazine, and he was in illustrious company, the same issue contained a short novel by De Camp and a story by Leigh Brackett.