With bitcoin, I'm kinda sure there was never any certainty, only faith; for a few, that worked out very well. But bitcoin has always been a gamble, a very unstable and easily influenced investment product, with unsafe and corrupt trading platforms.
I didn't have any magical crystal ball, like no one else did. The key transition point was moving the Bitcoins into the Ethereum. For me, Vitalik's early posts convinced me that Ethereum wasn't just another altcoin and it had great potential.
I didn't have any debt at that point and the traditional model of saving portion of salary and getting 4% annualized growth wasn't going to achieve the wealth I had in mind. So cryptocurrencies seemed like it had the huge upside potential I wanted and the worst-case scenario would have been that I'd lose the initial 20k€. I'm fairly opportunistic and risk-seeking. YMMV.
Hard to say what the probability of failure (ie. Bitcoin collapsing or the value of Ethereum being far less than the pre-sale price) has been.