The best analogy I can find on how technical analysis can improve your investing is a roulette wheel. I use this analogy with reservation, as gamblers have very little control when compared to investors (although considering the actions of many investors, gambling may be a very appropriate analogy).
"There are two times in a man's life when he should not speculate: when he can't afford it, and when he can."- Mark Twain, 1897
A casino makes money on a roulette wheel, not by knowing what number will come up next, but by slightly improving their odds with the addition of a "0" and "00."
Similarly, when an investor purchases a security, he doesn't know that its price will rise. But if he buys a stock when it is in a rising trend, after a minor sell off, and when interest rates are falling, he will have improved his odds of making a profit. That's not gambling--it's intelligence. Yet many investors buy securities without attempting to control the odds.
Contrary to popular belief, you do not need to know what a security's price will be in the future to make money. Your goal should simply be to improve the odds of making profitable trades. Even if your analysis is as simple as determining the long-, intermediate-, and short-term trends of the security, you will have gained an edge that you would not have without technical analysis.
Consider the chart of Merck in Figure 1 where the trend is obviously down and there is no sign of a reversal. While the company may have great earnings prospects and fundamentals, it just doesn't make sense to buy the security until there is some technical evidence in the price that this trend is changing.
