If you're either a passbook saver or a speculator, then you can benefit by expanding your horizons. If you're risk-averse, consider investing in a diversified portfolio of high-quality stocks - and hold them for the long term. Established companies may not soar like today's hot Internet stocks, but they generally don't crash and burn, either. And they will certainly provide you with a higher return than a portfolio composed solely of bonds, CDs, money-market accounts and Treasury bills. If you have trouble shaking your fear if price volatility, take comfort in this fact: Studies have shown that the longer you hold a portfolio of stocks, the less chance you have of ever losing any money.On the other hand, if you are more of a speculator, and you never met a risk you didn't like, you could still pick up a thing or two from the passbook savers. Remember, many of yesterday's "hot" stocks are today's unhappy memories. You, too, can benefit from building a diversified portfolio - even one that contains decidedly "unglamorous" investments such as large-company stocks and bonds.The passbook saver and the speculator each represent an important goal - security and growth. And we all need elements of both in our investment portfolios. The challenge is to go beyond our natural preferences and see what we can learn from those people walking on the "other side of the street."