When we see that red especially big red on the chart, that will be the best time to buy. The Bitcoin price will be back to the high price and give us the profit. So that's why the investor willing to buy more and more to have many Bitcoins. Those new investor really need to learn more if they don't want to panic seeing the market moves into red.
We may never know where the bottom is, but we surely know where the dip and the correction is taking place.
And as you said - it would be good points of entering, but there would be no ideal points due to what I described above.