As I approach age 50 and recollect 30 years of post-childhood lessons learned, I recognize a pattern I’ve lived through a few times.

I’ve learned that times of economic expansion have tended to teach me fallacies. It was easy to think I was a good bet-taker when every bet paid off. Until it didn’t.

Since the last recession and stock market bottom in 2009, it’s hard to find something that hasn’t appreciated incredibly. Someone who came of age during this period may build a flawed investment playbook developed over the good times.

History has taught us that our playbooks will eventually get tested once our upward cycle ends and a downward one begins.

Because this has been the longest period of economic expansion in modern history, I believe the number of fundamentally-flawed playbooks circulating thanks to the prevalence of social media is staggering: from flawed investment strategies to fallacious career advice to unsound life guidance. What has worked may abruptly stop working.

I hope 20- and 30-somethings who’ve experienced adulthood in a post-2008 era are careful not to fall for these transient playbooks.

My humble advice to you if you’re in that age group is to seek advice from an experienced mentor, not to count on your playbook until it’s been tested in a down cycle, and not to risk what you’re not willing to lose: your life savings, your career, your reputation, your relationships, or anything else that’s important to you.