Analysis
The phrase appears on several quote‑aggregation websites attributed to King, but none provide a primary citation such as a newspaper transcript, video, or published interview from the 1970s. A review of King’s biographies and archived sports interviews from that decade does not contain the wording. Without a verifiable primary source, the claim cannot be confirmed.
Background
Billie Jean King frequently discussed confidence and mental toughness in public, emphasizing self‑belief as key to success. While her general sentiment aligns with the quote, the specific wording is not documented in contemporaneous sources, suggesting it may be a later paraphrase or misattribution.
Verdict summary
No reliable source confirms that Billie Jean King said this exact quote in a 1970s interview.