Invest when you already sets all the plans, it's tough to rush when you see unexpected fall, you'll be temp to sell with losses.
If you are planning to invest at this rate then when the market reverses they will sell off at a loss and the main point they need to understand is that if they are willing to take risk then they need to be willing to hold for a much longer time if the market reverses rather than selling off at a loss and if that is the mindset then they can invest at any market rate.