Very proven, Yes. Holding bitcoin for longtime proves to be one of the best ways to grow money we have. Very much compared to interest given by bank.
Holding is no doubt a very good option for making a very good amount of money. If you have control over your nerves then this is the best thing which you should do. Holding of bitcoin gives you a guarantee of this thing that with each passing day, more amount of money will be added to your account. So you have to be very careful and you need to control yourselves especially at the hard times.