The Russian Ruble is highly correlated with the Russian stock market, that means an inverse correlation with USDRUB . I believe that the Russian stock market is looking (I have published a chart months ago) and that would mean USDRUB will go down. So you have the capital inflows to the stock market with you on this trade.
The USDRUB is highly correlated with the Dollar Index , which at the moment doesn't look good at all. It actually looks like the strong move has ended and at least a correction is coming, if not a total retracement. However, I would go with correction. So you have the weak dollar with you on this trade.
The interest rate in Russia is 8%. That is absolutely huge. The carry you earn by keeping a short will probably add up to more than the profit coming from the trade itself. So you have the excellent carry with you on this trade.
How can you not buy some Rubles, when you have all these factors working with you??
And for your information, Mr Trader, USDRUB has been my best trade ever.
There are no indications that USDRUB will stabilize anytime soon.
Ruble is going down with flames. If you buy rubles now, you will be going in flames too.