Quote from scriabinop23:
It is all statistics.
You could ask the same question about weekly performance expectations. Just increase leverage and flip a coin.
The problem with your question is that you can superimpose performance on any timeframe, and realize it is always comparing apples to oranges. I can double a $5000 account in a few days with the right run of luck. But just as often, I'll lose it.
Same goes for lower magnitudes of risk - if you aren't levered, you usually must settle for lower returns. If you are position trading, you must let your good trades perform enough to offset all of the bad ones. With that said, performance targeting will just as likely add another barrier to success (or at least a complication). If you were high beta going into mid-08 with 100% exposure, the odds are you lost 75% of your money. You need 300% just to get back to square one. 20% performance targets just don't cut it with that type of drawdown.
The point is simple: even if you never had that 75% drawdown, there's nothing stopping that from happening next year.
The whole thing falls in the realm of statistics and common sense -- if you are able to make 40%/yr on 250k without drawdown, then you have a special sauce that falls outside the parameters of this discussion. But if you make 40%/yr b/c your risk is beefed up and you can't precisely quantify why you've done so well, you have no advantage, and will always be on the precipice of failure. It's just a matter of time.