Editor's Note: Arne Alsin's column runs exclusively on RealMoney.com; this is a special free look at his column. For a free trial subscription to RealMoney.com, click here. This article was published Jan. 14 on RealMoney.

You should always be looking for ways to become a better investor. Great investors are obsessed with improving their skills. The idea that you've "made it" or that you have it "figured out" is nonsensical -- and dangerous, too.

In this two-part series, I'll discuss eight common sins (four today, another four in my next column) that I see many amateur investors committing. If you commit some of these sins, as I have in the past, sooner or later you'll suffer the consequences.

    The sin of impatience. Impatience is something I've struggled with as a pro. I now invoke my "Dayton-Hudson" rule when I know I'm holding a gem from the bargain bin: patience, patience and more patience.At the beginning of 1995, I found a nugget in Dayton-Hudson stock and made it my largest position. After I waited nine months for the market to see what I saw, my impatience led me to give up with a break-even trade and move on. The rest is history. Dayton-Hudson has long since changed its name to Target (TGT) - Get Report, and the stock is up sevenfold in the seven years since I sold. I've learned one very expensive lesson. If you get the story right, it doesn't matter if the market misprices your stock. Eventually, given enough patience, fair value will be realized. Last spring, my largest position, Office Depot (ODP) - Get Report, dropped 15% because the company announced it was going to miss earnings estimates by a penny. I knew I had the story right; it was just a matter of patience. Since then, the stock has more than doubled. The sin of overmanaging. I'm constantly startled by how much most investors overmanage their portfolios. I regularly get emails from readers who have invested in one of my stocks, only to exclaim, "Your stock is down 7% today on heavy volume!" Relax. This is a marathon, not a sprint. The average New York Stock Exchange stock fluctuates 50% a year. There's no need to change your portfolio frequently in response to the natural volatility of the market. There's also no need to have to "do something" in response to volatility in stocks. Buy quality companies in which a wide disparity exists between stock price and the underlying business value, and leave it at that. Don't waste your time staring at the quote monitor, and don't worry about minor ups and downs in your stocks. If you have the story right, time will be your friend. The sin of overtrading. Overtrading your account is a sure avenue to mediocrity. The formula is straightforward enough: Even though commission costs are heavily discounted nowadays, if you trade frequently, you'll still lose significant capital due to the slippage caused by the bid/ask spread. Do the calculation on your next trade -- whether you're buying at the ask or selling at the bid. The cost of the bid/ask spread is material for the frequent trader. Taxes are a huge cost as well. For taxpayers in high tax brackets, combined state and federal income taxes on short-term trading gains can amount to 40% or more of their profit. If you acted on my picks of Office Depot, J.C. Penney (JCP) - Get Report or Hasbro (HAS) - Get Report last year, you would have paid just one commission on each (to buy), incurred one slippage cost and paid zero tax. (We haven't sold yet!) When we do sell (don't hold your breath on this one), it'll be taxed at long-term capital gains rates, not at the much higher short-term capital gains rates. The sin of superficial research. If all you're going to do when researching a stock is to read the company summary and check the price-to-earnings ratio, stop right here. You might want to get some help. At a minimum, investors should be familiar with both the current financials and several years of historical financials before investing in a company. Don't skip the footnotes, by the way. They're generally the most important part. Familiarity with the company's peer group is imperative, and so is an assessment of management's capability.

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Commissions + Slippage + Taxes = Mediocrity

Sound a bit arduous? Of course it is. Being a successful part-time investor is just as difficult as being successful, part-time, in other professions. You have to be obsessed to succeed. The investment world is ultra-competitive, with plenty of smart people all vying to achieve the same objective. If it were easy, though, it wouldn't be any fun, would it?

Be sure to check out

RealMoney.com

later today for the second part of this column.

Arne Alsin is the founder and principal of Alsin Capital Management, an Oregon-based investment advisor specializing in turnaround situations. At time of publication, Alsin and/or ACM was long Office Depot, J.C. Penney and Hasbro, although holdings can change at any time. Under no circumstances does the information in this column represent a recommendation to buy or sell stocks. Alsin appreciates your feedback and invites you to send it to

arne@alsincapital.com.