If you're a longtime reader of Private Briefing, you know that I'm a "collector" of investing adages and aphorisms - you know, things like "Bulls make money, bears make money - but pigs get slaughtered" ... or "Buy on the cannons, sell on the trumpets."

These long-held sayings are usually clever, are often amusing and are always easy to remember. So they serve as an effective way for us to remember some important keys to investing success - or a fatal mistake that we need to avoid.

One of my favorite tech-investing adages holds that "You can always spot the pioneer - he's the one with the arrows in his back."

In short, if you're going to invest in a company whose technology is truly on the cutting edge, make sure your research is solid. Be as certain as can be that the technology isn't ahead of its time, and will find a market. And, lastly, make sure that the company you're seeking to invest in isn't about to be leapfrogged by a better, or more-market-friendly, technology.

As you can see, investing in a leader can be a tricky business - especially one with gargantuan market share. For one thing, when a company has a dominant market share, the odds that it's going to gain share are slim - meaning the best it can do is to hold the line.

And when a company is the "king of the mountain," it has a bull's-eye on its back. Everyone is gunning for it. So the most-likely scenario is that it will start losing market share.

That's because one or both of two things will happen. Rivals will start offering similar products, but at lower prices. Or those rivals will design new products that will leapfrog the dominant company's offerings.

I watched both of these play out against Eastman Kodak Co. (PINK: EKDKQ) starting in the middle 1990s. At one point, it had a reputed 90% share of the U.S. photographic film market. And let's be honest, where do you go from there?

Soon, Fuji Photo Film Co. Ltd. (PINK ADR: FUJIY) started eating Kodak's lunch, offering an equal product at a much lower price. Kodak alleged Fuji was using a "profit sanctuary" in its home market of Japan - where restrictions kept Kodak from effectively competing - to "dump" consumer film here in the U.S. market. Kodak even filed a case against Fuji with the World Trade Organization (WTO) - though it ultimately lost.

Fuji eventually set up shop in Greenwood, S.C., and before you knew it, Kodak's market share was down in the 60% range. The emergence of digital photography - which Kodak had an early stake in, but lacked the culture to effectively win against companies like Canon, Hewlett-Packard and others - pretty much ended the Rochester, N.Y.-based company's days as an industry heavyweight. It's now in bankruptcy.

Given what we've just talked about, when you see a noted market leader that's gaining market share, make sure you take a serious look. This is probably a stock you really want to consider.

And that's just what we've found with EMC Corp. (NYSE: EMC), the storage-and-security giant that we recommended in the Sept. 13, 2012 special report "Big Trends Equal Big Profits."

In that report, we predicted that EMC would continue to gain global market share in its core disk-storage market - putting distance between it and its rivals.

And that's just what's happened.

New research by Piper Jaffray Gartner shows that EMC's market share reached a record 34.2% in the fourth quarter, meaning the Hopkinton, Mass-based tech firm is expanding its already-hefty lead in this key market.

And external storage is just one of its areas of focus.

EMC is also boosting its business in the area of data security. And as we've told you in our "Cyber-Hacking of America" reports, this focus - coupled with its existing relationships with big companies and with government agencies -- will make EMC a big beneficiary of the cybersecurity-spending explosion. Indeed, EMC is on the prowl for security-related acquisitions. And unlike most firms, EMC has shown it knows what to do with companies that it buys.

Although the storage business hasn't been terrific, EMC still turned in a record fourth quarter - even reaching the $6 billion in quarterly revenue mark for the very first time. It hit that mark thanks to growth of 8% on a year-over-year basis and 14% on a sequential basis.

Some analysts have been worried that Oracle Corp. (Nasdaq: ORCL) - a rival of EMC's in certain areas - might be gaining ground. But Oracle reported a big revenue miss yesterday, and its stock was down more than 8% in after-hours trading.

EMC CEO Joseph M. Tucci said his company "remains squarely at the center of the most disruptive and opportunity-rich shift in IT history, propelled by the benefits of cloud computing, big data and trusted IT. These high-priority IT spending areas are core to our strategic focus and represent market segments where EMC has established leadership positions and competitive advantage."

As readers also know, we are very partial to stocks where we see the potential for more than one catalyst to ignite a rally. And that's certainly the case with EMC.

It already owns 80% of virtualization firm VMware Inc. (NYSE: VMW). Now those two companies are looking to generate growth and unlock value by spinning off a venture called "Pivotal Initiative" - a "mash-up" of "Big Data," analytics, and other related elements that currently sit inside EMC and VMware.

Though no time frame was established for an initial public offering (IPO), Pivotal is expected to be a standalone venture by April. EMC's discussion of this plan at a recent "strategy day" was extremely well received by investors.

The Pivotal businesses had revenue of $300 million last year. But company officials say it can grow to become a $1 billion business in five years - and said that may be a conservative estimate. The market at which this venture is aimed will be about $8 billion this year and is expected to exceed $20 billion by 2017.

EMC would take two-thirds of the revenue, while VMware would get one-third.

Tucci, the EMC CEO, said that "with our ambitions, we are facing giants" like Oracle, Microsoft Inc. (Nasdaq: MSFT) and International Business Machines (NYSE: IBM). But, by creating Pivotal, and having it work with EMC and VMware, "we can get a lot of benefits."

Sounds to us like Tucci has a plan to be very aggressive, and stay ahead of his rivals - without getting arrows in his back.

And that's the kind of profit play we like to find.

[Editor's Note: Unless otherwise specified, we advise investors to maintain a 25% "trailing stop" on all holdings.]