This advice "Only invest an amount you can afford to lose" is something that makes me shudder whenever I hear it.
Why? Because it is really not good advice for me. Of course, it is important to remember that all investments involve risks, but should you just put money into something you're willing to lose? Please, please, please. The same as saying "don't put money into it or do not invest!". I don't want to risk losing the money I have put in. Taking measured risks is something I am willing to do.