Valuation isn't cyclical to a degree where prices are required to decline as much as they increase to satisfy laws of symmetry.
It could as easily go to $2,000 and we'll never see $300 or $600 again.
Just as we never saw a $12 BTC again after the price rose above that point.
This! Its pure economics, and there is no certainty. The question though was whether he should invest the 1k Euro, and he alluded to the fact that it was a lot of money for him. Therefore, it would be unwise to invest any amount you consider to be a lot for you as you there are no guarantees whatsoever.