Hello Mr Kohei,
No signal (as SuperTrend is a signal) will guarantee profit in the future. Whether it does or not depends on how you implement it (much more can be – or has to be done around a signal for purchases at the correct moment). Also, no “trading” can depend on a few days only. Thus, the fact that you saw a loss of USD 837.5 in the period of 3 days, does not tell at all that the loss will be 8375.00 in 30 days. It could be -15000 but it also can be +20000.
I am not sure whether this is the kind of answer you expect. If not, possibly you can elaborate somewhat more ?
Kind regards,
Peter