Most successful investment strategy is buy when everyone is selling and sell when everyone is buying which can be long term or short term but definitely it is the most successful one.
A more successful investment will be the purchase of coins at the stage of a private or seed round, when the coin is sold at a big discount. The next stage of the purchase, when you can profitably buy a coin, is the stage of public sale, but this price will be several times higher than the one at which early investors bought.