It sounds like you're new to the sharemarket. At any point in time, a company's share price (SP) reflects two key factors:
1. Fundamentals - the company's ability to generate a stream of future profits/returns for shareholders; and 2. Sentiment - the market's general appetite for investing in shares, which reflects numerous regional/national/global forces.
The second factor is why the SP can dive even when the company is doing great.
