I hate that statement. Because people who say it claim they were right based on it, when they were clearly wrong and just trying to excuse their failure.
Saying 'at some point in the future prices might be lower' without a time attached to it is an intellectually empty statement.
The thing to understand about shorting is that your losses have no upper bounds. You short a stock at $100 and it goes up to $1,000, you now OWE $900. Here's [0] a story of a guy going to bed with $30k in his ETrade and waking up to a $106k debt call.
Be very careful betting on the market going down. You not only have to be right, you have to be right soon enough.