The equity risk premium is the best-known example, historically estimated in the range of three to six percent a year depending on the market and period measured. Estimates vary widely because the sample is short relative to the volatility of the series.
Premia are expected, not promised. Decades of underperformance against cash are possible and have occurred, which is precisely why the compensation exists: if the reward were reliable it would be arbitraged away rather than paid.
Other premia include term premium for holding longer maturities, credit premium for default risk, variance risk premium for selling volatility, and illiquidity-premium for accepting lock-ups. Each is a description of a risk being borne, and each can be negative for long stretches. See factor-investing.
Related: factor-investing, illiquidity-premium, capital-asset-pricing-model, efficient-frontier, volatility-arbitrage, beta