If price is below the 20 EMA, our bias is short and we would be looking for price to move up and hit the 20 EMA, reject and then move down.
However, if price pierces the 20 EMA and closes convincingly above it, we deem price to have switched polarity and now our bias changes to long. (This can be seen occurring at the right of the above picture). From now on we would be looking for price to move down and hit the 20 EMA, reject and then move up.
An example of one definite and one possible losing trade: