We all think we know what a shareholder is: an individual or entity that owns shares of stock in a publicly traded company.

It sounds simple enough. But let's think a little deeper about who -- and what -- shareholders are -- and what that means for your portfolio and for society at large.

We're everybody
Shareholders, after all, run the gamut. Some are huge institutional investors that buy up millions of shares for other people's portfolios. Some are individual investors, many of whom are trying to fund their retirements by buying shares in small lots.

Some shareholders, like Warren Buffett, buy shares based on clear investing theses. Others fall so deeply in love with a company and its stock that they can't bear to hear anything negative. Don't believe me? Just look at some of the conversations around stocks such as Apple (Nasdaq: AAPL), Sirius XM (Nasdaq: SIRI), and Crocs (Nasdaq: CROX).

Some shareholders prefer to restrict their investments to their portfolios, while some investors want to get involved with the company itself. Recall Carl Icahn's involvement in the talks between Yahoo! (Nasdaq: YHOO) and Microsoft (Nasdaq: MSFT), for example. Unions and political organizations often buy stakes in publicly traded companies so that they can try to encourage change as well.

Activist shareholders don't always have the best long-term interests of businesses in mind, of course. Sometimes, they're focused more on making a quick buck or a political point. For the most part, however, I'd argue that activist shareholders have something to teach the rest of us -- particularly in their focus on being "part owners" of the companies they invest in.

More than just short-term profits
Jack Bogle, founder of Vanguard, recently talked to the Fool. He pointed out, as he often does, that the stock market and its daily gyrations can be a major distraction from the real basis of investing: finding great businesses that will earn a return on capital over the long term.

When shareholders are focused on the fundamentals -- earning a return on capital and creating great businesses -- they're attentive to the choices being made and the money being spent -- and earned. But when shareholders are focused only on the daily gyrations of the share price, they end up tolerating "management culture."

Management culture is nothing more than the tendency to run a company for short-term profits, a strategy that enriches only the management team and all too often destroys real value over the long term.

And we've seen its outcome. While many things contributed to the fall of the financials, a focus on short-term "profits" -- with many CEOs, even departing ones, enriched immeasurably -- over long-term, sustainable practices, is one of them.

Just look at John Thain, CEO of Merrill Lynch before Bank of America (NYSE: BAC) swallowed it. Thain redecorated his office with rather decadent zeal. Call me crazy, but even if Merrill hadn't been in dire straits, a $1,400 trash can should have been viewed as a heinous waste of shareholder money. That's not exactly capital being utilized to build a solid business.

That trash can is a powerful metaphor for the way managements too often completely forget who they work for.

We paid for that!
Why have we tolerated management that wasted money, that didn't concern itself with the shareholders, and that focused on the short term instead of the long term? Because we don't consider the philosophical difference between being a speculator and being an owner.

I think that if we took our role as part owners more seriously, many of the problems we've seen recently might not have happened -- if only because managers would have known investors were looking at the long-term results, not the short-term stock price.

No, shareholders don't get to make management decisions -- and we shouldn't. But we can pay attention, and we can ask questions if we see something that doesn't support the long-term success of the company. We can vote our yearly proxy statements, and we can attend shareholder meetings. And if we have to, we can make statements by selling our stock.

Even though we want to profit from our investments, we must shoot higher than just passively looking to make a short-term buck. We must invest in truly great companies while having the patience to let solid management teams build sustainable businesses for the long term -- and agitate for change if they don't.

Let's just remember that management works for us.

Make it a good century
Shareholder-friendliness is one of the characteristics we look for at Motley Fool Stock Advisor. But it's not the only one. We also look at whether the company is built to last for the next 100 years or more -- and that means looking for solid, innovative businesses with great brands, strong balance sheets, and responsible management teams that take their responsibilities to shareholders to heart.

It's those kinds of characteristics that get great businesses such as Berkshire Hathaway (NYSE: BRK-A) on the Stock Advisor scorecard.

Any of us can run into pitfalls in assessing these things. For example, maybe a company's management isn't as solid as we believe -- that's what occurred with former pick Satyam. But it's important to ask the questions and remember our own responsibilities in assessing the long-term attributes of the companies we own.

Let's not be mere speculators who look at nothing but numbers and never care about the real things that create tangible value. Let's revive the philosophy that a shareholder is an owner, and let that responsibility be a prevailing theme in our investing strategies. You don't get better results until you expect better behavior. And stronger shareholder resolve and involvement can hopefully help us all be part of building the best companies for the long term.

If you'd like to see what shareholder-friendly companies we're currently recommending at Stock Advisor, you can take a 30-day free trial -- and our recommendations are currently beating the S&P by 30 percentage points, on average. Just click here to get started -- there's no obligation to subscribe.

Alyce Lomax owns no shares of any of the companies mentioned. Berkshire Hathaway and Apple are Motley Fool Stock Advisor picks. Microsoft and Berkshire Hathaway are Inside Value recommendations. Bank of America is a former Income Investor choice. The Fool owns shares of Berkshire Hathaway and has a disclosure policy