"it will almost certainly double in value in 7 years" implies 10% is an almost certain long term return. It is not.

10 years is a common rule of thumb to double your investment, this is a good guess since after adjusting for inflation, the real return of S&P 500 is about 6.8%. Which is about 10.5 years to double your investment.

(give or take S&P 500 being one of the best returns you will find historically)