Just tell him about the probabilities of price cant reach on a specific range but since everything is unpredictable then theres always a 50% chance for it to happen.
So its up to him if he would wait or sell out on point because each one of us does have its own criterias before making any decision towards our investmentment.
the market then its really hard to decide and you are right that we do have our own choices when we do make out decision.It isnt an easy stuff specially on the times when our mind do tell to sell but our
feelings inside do tell that we should wait for a little more and hoping for more price increase.So this one will vary to person to person.