It's not a guarantee that hodling bitcoin for years will prevent its price from falling to a point where it's affordable to purchase during a bear market since the bear market serves as an opportunity to buy bitcoin at a low price.
holding Bitcoin will never withhold or prevent the Bitcoin price from falling because holding has nothing to do with Bitcoin price and perhaps that's not even the reason of holding. We know how Bitcoin price can be very volatile sometimes so the only way we can keep our mind at peace is by holding because if you decide to chase the price movement you could end up getting cut by the market.
Also one of the factors that always affect an investor from accumulation of Bitcoin is always expecting the Bitcoin price to dip before they could start accumulating, considering the price movement of Bitcoin waiting for the dip may not be advisable because you could be waiting for a long time and the price is still not dip.