Have you ever tried to read a life insurance illustration? Often times they are so complicated that only a seasoned agent can understand them. They have all the disclaimers on them about returns and typically you will see at least two columns of projections.
One column will be the guaranteed column, which will be the worst case scenario. The other column is the assumption column. This is usually based on the companies current dividend scale or some type of hypothetical return. It is important to look at what guarantees are built in and to look at the companies historical results. If you have a dividend paying whole life product, the dividends will go up and down. The dividend is based on the companies success and the success will obviously fluctuate over a long period of time. Most good mutual companies have never missed a dividend, but the amount of the dividend is the key. If you are talking about a universal life, there is a bottom floor interest rate or return level in one column. Many plans might guarantee like 3 or 4 percent as a worst case scenario. The other side will be some hypothetical interest rate or market return. This like the dividend is a total guess based on some historical data and future projections.
The key to reading an illustration is that it will give you some rough parameters. Just remember that it will never play out exactly as illustrated.