What’s the biggest threat to a comfortable retirement? Ignorance. The decisions you make leading up to retirement, including how much to save, how to allocate your investments, when to take Social Security and how to anticipate your retirement expenses can make a big difference in your old age. And the decisions don’t stop on Day One of your post-career life. Once you’re in retirement, you’ll need smart strategies for taking withdrawals and investing your resources so they last as long as you do.