The stock market is a complex system that is influenced by a wide range of factors, both internal and external. These factors can cause shares to trend upwards or downwards. Some of the key factors that can impact share prices include:

1. Economic conditions: The overall state of the economy can have a significant impact on share prices. Positive economic conditions, such as low unemployment and GDP growth, can cause shares to trend upwards.

2. Company performance: The financial performance of a company can impact the value of its shares. Strong earnings reports and positive news can lead to an increase in share prices, while poor performance can lead to a decrease.

3. Industry trends: The performance of a particular industry can also impact share prices. Positive trends in a specific sector can lead to an increase in share prices for companies in that sector.

4. Market sentiment: The overall sentiment of investors can also impact share prices. Positive news and investor optimism can cause shares to trend upwards, while negative news and pessimism can lead to a decrease.

5. Political factors: Political events and policy decisions can also impact the stock market and share prices. Changes in regulations or geopolitical instability can cause uncertainty and lead to a decrease in share prices.

Overall, a variety of factors can impact the value of shares, and investors should consider these factors carefully when making investment decisions.