The hard part with waiting for too long is the uncertainty that the price is going to reach your buy target. If the price eventually reaches $5,000 and you though that the current price of $2,800 is too expensive, then you would have lost about $2,200 in profit because you didnt jump onboard. But that is all ifs and buts and we really dont know if the price would still be bullish in the next few years or it would succumb to the bears and go down again below $2,000.
That's why a bunch of people in this forum state that an investor should only invest the money that they can afford to lose because the price of Bitcoin is not a for sure thing and the price of Bitcoin is very likely to go up instead of down. Investing small amounts into Bitcoin allows the investor to make money if the price goes up without worrying about the regrets of not investing sooner.