The only secret that you should know is buy the dips (Bitcoin dips not altcoins), once you see a big dip in the market be rest assured that there will be a pump.
You are right but it is good to know that the market can be deceiving, although not frequent but possible that after a big dip the market will show sign of increase. After the market increase a little, the price of the coins will start to fall again even more than the last dip. Especially the altcoins, we need to be very careful of them.
For the record, I mentioned bitcoin specifically because I know even if it does fake an increase before it's price correction fact remains that profit is inevitable.
It's obvious if studied from previous performance and patterns which bitcoin had push through, and although we can't be specific about bitcoin nowadays because it could be possible that it has changed patterns since it has reached a good number of mined coin.
You're right, no matter how low bitcoin goes during a market dip, investors must still stand a chance of gaining later, that's why it's good for long-term investment and not short-term and the best thing an investor would do to their portfolio is accumulating more bitcoin even though it dips again after an increase, see it as more chance to accumulate more.
If investors take their time to research about the history of bitcoin and it's behavior during every circle it's gone through, then they'll know that it's the best crypto asset to invest on during every market dip and accumulating more is the best option at that period.