Sure bets mean something that is considered certain or almost guaranteed to happen. However, its antonyms present a different story altogether. Some of the antonyms for sure bets could be risky, unsure, unpredictable, speculative or dubious. In the world of investments, a risky option may not be a sure bet for a high-profit margin. Whereas, the unsure or dubious option may be an opportunity that could either lead to immense gains or significant losses. Unpredictable options, on the other hand, may yield results that are different than expected. In short, sure bets, when used with antonyms, present the other side of the coin and highlight the uncertainty or risk involved.