BabyGeezer:
ehm... isn't that the basis of the scientific method ?
you don't know - but you guess* what it is, and then that guess is either validated or proven wrong, at which point you will then DO know (something).
- = educated one, conjecture or theory...
Science is about explaining and predicting observed/observable/measurable phenomena - coming up with plausible/backable theories to explain the mechanisms behind the observations. It is built-up on accumulated scientific knowledge - (math, gathered data, physics, chemistry etc).
Switching over to something else (eg. nrf24L01) when the existing device (hc-05) is expected to be workable is certainly an option. But, naturally - it is definitely advantageous to find out the reason(s) for a particular approach being currently unable to achieve your objective ----- which is why you asked about it, and which is good. This enters the area of electronics/electronic engineering, and working towards improving electronics knowledge and skills.