(Image credit: Getty Images) It can be exhilarating. The market goes on a tear, your portfolio's value soars, and, perhaps, a part of you thinks it will always be that way. Until one day, that marvelous portfolio balance isn't so marvelous anymore. From just $107.88 $24.99 for Kiplinger Personal Finance Become a smarter, better informed investor. Subscribe from just $107.88 $24.99, plus get up to 4 Special Issues CLICK FOR FREE ISSUE Sign up for Kiplinger’s Free Newsletters Profit and prosper with the best of expert advice on investing, taxes, retirement, personal finance and more - straight to your e-mail. Profit and prosper with the best of expert advice - straight to your e-mail. Unfortunately, that's when you discover — much too late — that you had even more of your money at risk than you realized. This is because that long-lasting, upward-trending market , with equities gaining in value, threw your investments out of balance. Here is why that is so.…