This article appears as part of Casey Weade's Weekend Reading for Retirees series. Every Friday, Casey highlights four hand-picked articles on trending retirement topics and delivers them straight to your email inbox. Get on the list here.

One of the most unsettling aspects of retirement planning can be the uncertainty that comes along with it. How long will you live? How will the market perform? How will your expenses change over time? These are questions we never know the answers to ahead of time, which makes incorporating them into your retirement plan all the more challenging.

Forecasting your financial future: How do you factor the unknown into your retirement calculations? Note the key variables highlighted in this article that can greatly fluctuate your retirement projections. They include: Investment returns, inflation, life expectancy, Social Security and expenses. A slight change in any of these conditions can significantly alter the output of your retirement plan’s performance. Additionally, utilizing best-case or worst-case scenarios for each variable alone – and even simultaneously – can be a shocking wakeup call at just how little control we have over certain potential pitfalls.

"Certainty" is Complex: Ultimately, the creation of your retirement plan will come down to utilizing guidance received from your financial advisor and gut instinct based on numerical probabilities, your values and what means most to you. Dialing in your expenses as you transition into retirement and throughout retirement will be the number one determinant of your financial success.