We've known for a while that traders tend to be their own worst enemies. This may be one of the more shining examples in recent memory.Robinhood is generally known as the trading platform of more inexperienced, less affluent investors. These folks can often get caught up in the latest news cycle and be influenced by the recommendations of friends and media.With oil being all over the news, it looks like that's exactly what happened with the United States Oil Fund (USO) in Robinhood. In this case, a lot of folks tried to catch the falling knife.The chart is a little misleading because it's not 1:8 reverse split adjusted, but you can clearly see the trend. Robinhood investors were adding USO to their accounts as oil prices were diving. Perhaps they were trying to buy the dip, but they certainly did it at the wrong time.And it wasn't just a few accounts either. USO went from very little ownership at the end of February to 60,000 accounts by the middle of April to more than 220,000 by the end of the month.All of that occurred as USO's share price was dropping from around $10 pre-split to its low of around $1.70.Here's the split-adjusted chart of USO so you can get a better sense of the real damage.The massive losses that many of these shareholders experiencing were made worse by the fact that they decided to cut bait just as things were beginning to turn around.The number of Robinhood accounts holding USO dropped all the way down to around 145,000, a decline of more than 30% in just a few days. And it happened just as the price of USO rose from just under $17 post-split on Tuesday afternoon to its peak of over $19 on Thursday.Unfortunately, we see a lot of this "buy high, sell low" kind of activity. Plunging oil prices over the course of just a couple of weeks proves again how dangerous both the markets and investor behavior can be.Try2BeFunded is expanding its trading program! If you're a novice or experienced trader, you can earn access to a trading account with up to $100,000! To learn more about how to qualify, click HERE.