When the calendar said one thing, and the chart screamed another on $GBPUSD
Had a classic setup on $GBPUSD a few years back, looked solid technically. Everything aligned: indicators, price action, you name it. The problem? I was so focused on the chart I completely neglected the economic calendar. It was a Friday, and a major UK GDP release was due within the hour. Of course, the market decided to treat my perfectly good technical setup like a punching bag, wiping out my stop and then some within minutes of the news drop. Left me wondering why I even bothered looking at charts if I couldn't even keep track of what day it was, let alone what data was dropping.
The lesson, painfully learned: technicals don't live in a vacuum. Fundamentals, or at least the market's reaction to them, can send the prettiest chart pattern straight to the bin. Now, the first thing I check when I'm looking at a major is what's coming out, and when. Saves a lot of grief, and a lot of capital.