Diversification allows you to recover from the loss of your total investment (20% of your portfolio) by gains of 10% in the two best companies (25% x 40%) and 4% in the remaining two companies (10% x 40%). Even though your overall portfolio value dropped by 6% (20% loss minus 14% gain), it is considerably better than having been invested solely in company E.
A stock's market capitalization (cap) is its true value, the sum of the total shares multiplied by price. It has more meaning than the share price because it allows you to evaluate a company in the context of others of the same size in its industry. You can use a market cap as a filter to screen for companies to balance your portfolio. A small-cap company with stock capitalization of $250 million to $2 billion shouldn't be compared to a large cap, which ranges from $10 billion to $100 billion. Market capitalization influences your investment returns. 

Intuitive Surgical (NASDAQ:ISRG) -- Intuitive Surgical is a healthcare company that makes surgical robots and is the clear leader in the space. There are tens of thousands of doctors trained on the company's da Vinci surgical robots and more than 4,400 of the robots installed worldwide. As more surgical applications are found for the technology, these machines become more valuable to the hospitals that own and use them.
The two types of brokers are full-service and discount brokers. Full-service brokers tailor recommendations and charge higher fees, service charges, and commissions. Once an account is set up, a discount broker can allow you to do it yourself at minimal cost through their website and offers support online, by phone, or in a branch when needed. The cost of buying continues to decrease with the introduction of apps. Apart from cost, a distinguishing factor is the research provided.
Imagine owning stocks in five different companies, each of which you expect to continually grow profits. Unfortunately, circumstances change. At the end of the year, you might have two companies (A & B) that have performed well so their stocks are up 25% each. The stock of two other companies (C & D) in a different industry are up 10% each, while the fifth company’s (E) assets were liquidated to pay off a massive lawsuit.
There are also other reasons for putting out free stock picks. In many cases, the actual companies themselves are paying various people or services to tell the world about their business. It's common to have a small, publicly traded penny stock pay a lot of money to get the right kind of exposure to help lift their share price. The aim is to issue more stock at a higher price and raise money more easily.
Understand that for both beginning investors and seasoned stock market pros, it's impossible to always buy and sell the best stocks at exactly the right time. But also understand that you don't have to be right every time to make money. You just need to learn some basic rules for how to identify the best stocks to watch, the ideal time to buy them, and when to sell stocks to lock in your profits or quickly cut any losses.
Experienced investors such as Buffett eschew stock diversification in the confidence that they have performed all of the necessary research to identify and quantify their risk. They are also comfortable that they can identify any potential perils that will endanger their position, and will be able to liquidate their investments before taking a catastrophic loss. Andrew Carnegie is reputed to have said, “The safest investment strategy is to put all of your eggs in one basket and watch the basket.” That said, do not make the mistake of thinking you are either Buffett or Carnegie – especially in your first years of investing.

The least demanding way to invest in the stock market is to invest through a fund. There are two types of funds. First is the actively managed mutual funds which have higher fees—92% of these funds fail to beat the underlying index over any three-year period. The second type is the index tracking fund, which typically has lower costs and is more effective in matching the growth of the stock market. This means they are growing in popularity because of the higher return on investment you receive. You should also use the most tax efficient way to invest: using your Investment Retirement Account (IRA) first. It’s best to invest in a low-cost, index-tracking fund through your tax-free IRA.
In order to be successful at both stock trading and investing, you need to be patient and maintain your composure in every situation. The nature of work is stressful, almost hectic, and you are bound to be losing substantial amounts of money some days. It could be very tempting to try to recuperate your losses by “doubling up” on your gamble, or opening high-risk positions that were not a part of your game plan, but this is precisely what you should be avoiding. That does not mean you shouldn’t dynamically adjust your investment plan to fit the current market conditions—it just means you shouldn’t modify your plans in a rushed or disorganized manner while carrying an emotional burden.
At the same time, there are literally hundreds of thousands of individuals who buy and sell corporate securities on one of the regulated stock exchanges or the NASDAQ regularly and are successful. A profitable outcome is not the result of luck, but the application of a few simple principles derived from the experiences of millions of investors over countless stock market cycles.