Successful investing can be boiled down to one essential principle—prudently setting aside money over an extended number of years. But prudent investing does not necessarily mean no-risk investing. Many of us, for example, still think it is prudent to put our money in “safe” investments like Treasury bills. But historically, T-bills have yielded only one-third as much as stocks.

Why do so many people stay away from higher-risk investments like stocks? I think the fear factor is one reason. Another reason is that people do not stay committed to a long-term financial plan.

A common mistake investors make is getting discouraged by the small sum they accumulate in a few years and yanking their money out for a down payment on a new car. But the value of long-term investing is illustrated by an old riddle: “Which would you choose, $1 million or a penny that doubles each day for a month?”

Look at the penny after 10 days—it’s only worth $5. After 20 days, it grows to $5,00. But after 30 days, it’s worth about $5 million. Dramatic gains come in the last third of the month.

It works this way in real life, too. Your $20-per-week investment fund won’t look like much after 10 or 20 years. But when you pass 30 years, you will be astonished at its growth. The power of compound interest also plays a major role. Over 40 years, an additional 2-percent yield will double the size of your fund.

Sounds like a pipe dream? World-renowned investor Sir John M. Templeton averaged 15 percent a year on the first mutual fund he established in 1954. An investment of $20 per week in that fund since then would be worth more than $3 million today.

Sadly, in the early 1990s American investors had one-half as great a percentage in stocks as they did in 1968. In my estimation, conservative Christian had even less.

Stocks offer two primary advantages over other investments: (1) They have made more money than other asset classes. (2) They finance business, which provides jobs and helps our economy grow.

Naturally, investing depends on your goals and circumstances. If your child will enroll in college in a few years, you should avoid stocks; year-to-year fluctuations could hurt in the short run. Instead, place your savings in T-bills and certificates of deposit (CDs).

But if your time horizon is at least five years, recent history shows that investing in a broadly-diversified mutual fund has outperformed savings accounts.

Since the typical mutual fund invests in 200 or 300 stocks, this automatically provides the safety of diversification if a particular stock goes sour.

Where do you find the best funds? A favorite guide is Morningstar, morningstar.com. For purposes of safety, I advise smaller investors to select a fund with the flexibility to invest in any kind of assets anywhere in the world.

People often ask me how to divide their money between stocks and bonds. A guide is to use your age as a percentage of fixed-income funds investments. For example, a 25-year-old would put 25 percent in a bond or CD and 75 percent in the stock market. A 75-year-old would do the opposite.

A practical benefit to disciplined investing is that it is an exercise in spiritual training. It postpones immediate gratification for long-range rewards and show faith that the unseen future remains in God’s loving hands.