Let’s say someone you trust offered this deal. (Assume 100% chance both of you would follow through on the deal.) Would you do it?
You buy Bitcoin today. In one year, if Bitcoin has gone down, they pay you the amount of the loss, so you are whole. If it goes up, you pay them half of the gains.
In other words, you break-even or better. The “cost” to you is half of the potential gains, and locking up money for a year.