Again there is a toolkit... for the multi-faceted trader there are different types of trades: Trend trades, swing trades, income trades.
With a trend trade we would explicitly avoid profit targets (as is the nature of following trends). This is especially appropriate for potential large moves, as the best equity moves can ultimately result in 300% upside, 50% downside etc before basic trend parameters are violated.
With swing trades it can make sense to have targets. Say, for example, you have a high probability long or short entry at the top or bottom of a range. With this type of trade your objective is to capture a chunk of the range. So once you get it, you are out.
And then there are income / carry trades -- buying something for yield, limited risk credit spreads to take advantage of time decay etc...
Point being we take advantage of multiple approaches (while trying to stick with what we're good at). As far as prediction goes, that's another in-depth discussion in itself. We use prediction the way poker players use imperfect information at the table: To exploit favorable reward / risk situations.
There are too many shades of gray, and too many undefined areas, to say flat out whether prediction "works" or not. It's deep water but fun to swim in for certain demented folks (like yours truly).
