People, prediction is a general term. Many predictors come with accuracy estimates (and outside of finance, often prediction bounds). But even if it was only one number - if you have good prediction of the expected price change, that could be sufficient to trade as it encompasses, by definition, the sun of probability of different outcomes times their magnitude.

Either E[price] or E[log price] is a single predicted value you can successfully trade with as long as you are far from your margins, and depending of course on your utility functions.

But as I mentioned, in most fields, when you talk of a “predictor”, that’s not a single number but also accuracy estimates or even a full fledged probability distribution of future events.