Final answer:
High capital gains cannot be ensured by investing in highly profitable companies due to market efficiency, unforeseeable changes in market conditions and company performance, and investor expectations already inflating stock prices.
Step-by-step explanation:
A financial investor cannot guarantee high capital gains by simply investing in companies with a history of high profits. One key reason is market efficiency, which posits that at any given time, stock prices reflect all available information, including a company's profit record. Consequently, any potential gains from such information are already factored into the stock's current price. Moreover, future performance is not guaranteed to mirror the past due to variables such as market conditions, competition, internal company changes, and broader economic factors that can dramatically influence a company's profitability.