Utilize your financial knowledge, give your answer or opinion to the input question or subject . Answer format is not limited.

Why can't you just have someone invest for you and split the profits (and losses) with him?
On reflection there are financial products that do what you want, whole-life insurance policies that guarantee an annual dividend calculation on some index with a ceiling and floor.  So you will have a return within a defined minimum and maximum range.   There are a lot of opinions on the internet on this.  This Consumer Reports article is balanced These have a reputation for being bad for the consumer compared to buying term life and investing in a mutual fund separately, but if you want the guarantee (or are a "moral hazard" for a life insurance policy, closer to death than you appear on paper) it may be a product for you.   If you're very wealthy, there is an estate tax exploit in insurance death benefits that can make this an exceptional shield on assets for your heirs, with the market return just the gravy.