Every idea that loses money is a bad idea...

...but some leave you scratching your head from the start. Inspired by today's news that Playboy will no longer print pictures of nude women, here are three time-tested blunders. Don't make one this week.

3 - Picking bottoms and tops

Take a look at a long-term chart, find the bottom and then calculate how much money you would have made if you bought at that exact moment. Now calculate how much you would have made if you waited a few days/weeks to see if the trend was really reversing. It's worth it to wait.

2 - Trading without a plan

Gut instinct isn't a good companion in a trade. Have a good idea where you're getting in and out, or better yet, a detailed plan. Know the calendar, know the risks.

1 - Adding to a losing trade

"When in trouble, trade it double. If you're crippled, trade it tripled." That axiom is a joke. Nothing blows up an account like adding to a losing trade.