Greed does play a big role in losing money in anything. Like in gambling and investing. If you hold to long and never sell at even near the peak then you will likely just settle for a few percentage income or even for losses because you missed your chance when the prices were pretty high. I've experience this a lot of times, especially with bitcoins.
Greed may kill your profits but I am not ready to accept with the case of bitcoin holding, only people who are greedy, holding till date and other have booked profits at $800/$1000/$1500/$2000 levels itself. Still, they were not losing, but if they were greedy they might got another portions of big profits.