Hmmm, for me that best time to make a comeback is during crypto's pullback because the price is so cheap. Just look at bitcoin today, almost touching 5 digits again and the last lower lows was like $3k. So if you have invested that time then its already 3x by just holding.
Altcoin market is also recovering, might be a good time to join the bandwagon again early 2020 because once the market had recovered and go on a full blown bull run, regrets!!.
Most of the people or investors regret once they see the price touching their expectations but yet they did never invest at the point they feel only because they were too afraid to get into the coin at that movement. Fear should be controlled the same way we might control our risk. Even at the times when bitcoins were somewhat close to $3k they had to face some major pumps and dumps which might have made a lot of people to think that the price for bitcoins might even cross those limits and might be hard to recover which made them stay far from getting into.
But, for those people who afforded to make some research were the ones who got in at the correct time and now are bearing sweet fruits for their risk.