It would be a matter of accuracy then on his prediction. When you are trading, there is a higher chance of being able to predict accurately when you have a basis of your trading like when you use technical analysis or fundamantal analysis or the combination of both in which case the percentage of getting it right is higher.
You can also have the option to just buy a little bit of it in regular intervals so that you can have cost averaging. Through this way, you will not be affected that much by the price volatility and you can adjust your regular investment amount as well. Nowadays is a good buy but I don't suggest to buy it in a single price but in percentage.