Yeah its never smart idea to buy when price is high as it will kill your profits and its always good to buy when price drops and sell them when price goes higher and that is the best way to make profits and most of the traders are making profits in the same way.
That's everyone thinking about profit, buy at low price and sell at high price. But, the hard thing is when the best time to buy and sell. Because, I have seen everyday got trapped by market and loss their money with blindly to buy without thinking about the future.
Most people only thing that buy at low price is very profitable if they sell at high price, but at reality they bought coin at low price but the price keep go down, they buy without any prediction the price will go up again or keep down.
Yes and its awful , well there are no sure with market volatility bitcoins or altcoins more often it happens in altcoin but the best time isn't to invest and bought when price is cheap .I think the best time is when you are ready to face those actions and to earn or not .There's no best time as long as you can manage your investments and make profits in a time.