Your returns' dependence on 1 trade would lead me to believe that your strategy is not very robust (i.e. capable of withstanding a wide variety of market conditions, moves, etc)
As a quick and dirty estimate, a straddle implies a probability of profit of around 55% for the seller and 45% for the buyer. The seller of a straddle has to be compensated because of the unlimited potential risk it's facing (zero on the downside and infinite on the upside). Statistics show (and again, statistics are the past but it's the best we have) that in most situations (around a 10 to 15 percentage points edge) the implied move in earnings is OVERstated so it favors the sellers. Of course the actual move compared to the implied move is only one factor and the determinant of profits is a combination (position sizing, strategy, timing, exit strategy, etc)