"An investment portfolio should fit like a comfortable suit."
The above quote is the philosophy of one of my college professors. It's a philosophy I believe serves all investors well. It helps to assure the investor no matter what direction the markets take them.
Among the considerations for putting together this "comfortable suit of clothes", an investor should follow a process that takes into account their current situation, where they want to be in future, how long that timeline is, and of significant importance their ability to tolerate the ups and particularly the downs the markets will experience. This level of comfort ensures the investor does not lay awake worrying about their portfolio.
The advisor serves as the "tailor" by taking the above as well as other factors into account when designing and managing the portfolio. The end result is an asset mix (stocks, bonds, etc) that minimizes risks to acceptable levels while maximizing the returns. In short an appropriate portfolio ("comfortable suit") that serves the client in their efforts to reach their life goals.