Which factors signify changes in investor circumstances for individual investors?

Changes in investor circumstances for individual investors are primarily influenced by personal factors such as career, family, and health. These elements play a critical role in shaping an individual's financial situation, risk tolerance, and investment goals. For instance, career changes can affect income levels, which directly impact the amount available for investment or savings. Family-related changes, such as marriage, divorce, or having children, can also significantly alter financial priorities and future planning needs. Health issues may lead to increased medical expenses or influence the timeline for retirement.

In contrast, while market fluctuations, interest rate changes, and investment opportunities are essential external factors that can affect investment decisions, they are not reflective of the individual investor's personal circumstances. These external factors can influence market conditions, but they do not indicate a change in an investor's personal situation. Therefore, the answer focusing on career, family, and health accurately captures the internal changes in an investor's life that necessitate a reassessment of their financial strategies.