True. Those time frames with downtrends/drawdowns are mere squiggles on a chart when backtesting. Yet when you're in the middle of these periods real time with somewhat leveraged positions and caught reasonably underwater on these positions for weeks on end, then on can lose intestinal fortitude and make emotional trading mistakes.
In order to be a successful trader:
1) Do a couple thousand trades over a 10 year period,
2) Lose a large amount of money 2 or 3 times and scare the sh_t out of yourself
3)Have a big enough bankroll to comfortably ride out #1, #2