Behavioral Finance and Client Investment Decisions

In a recent client meeting, a wealth manager noticed that one of his high-net-worth clients displayed significant anxiety about investing in the stock market, despite having a long-term investment horizon. The client mentioned previous experiences of market downturns, which led to considerable losses, and expressed a strong preference for safety over growth. The wealth manager recognizes that this client's behavior may be influenced by biases related to past experiences.

Which of the following behavioral finance concepts is most relevant to address this client's concerns and improve his investment decision-making process?