I have heard this from others as well. Most of the times the experts say that buy low and sell high and use the profit to buy more at lower prices.
This indicates that we should never miss an opportunity to buy bitcoin at cheaper price as it is bound to bounce back to a higher price.
In my opinion, the price of Bitcoin goes down and stable is the best opportunity to buy and hold it for the long-term. And now, when the price of Bitcoin is stable at around $3,000, I think this is the best time to invest because Bitcoin can't go down under $3,000.