The bulls may want you to believe this, but no stock is safe.
There are businesses that may remain good (earning return on capital greater than cost of capital) for some time, maybe a long time, but you must not attach infinite values to them.
This is because high returns attract competition, generally causing return on capital to move towards the cost of capital. While such companies may still earn excess returns, but the return trajectory is down.
Everything in this world, after all, is momentary. So, your best bet is to just stick with quality (even that is momentary, just for longer moments that allows time for compounding to work its magic).
The good thing about high-quality stocks is that you can pay up for them (never overpay), expensive looking prices, and still do well till the underlying businesses remain good.
With poor quality, most probably, you have no hope.
As Charlie Munger says –
Over the long term, it’s hard for a stock to earn a much better return that the business which underlies it earns. If the business earns six percent on capital over forty years and you hold it for that forty years, you’re not going to make much different than a six percent return – even if you originally buy it at a huge discount. Conversely, if a business earns eighteen percent on capital over twenty or thirty years, even if you pay an expensive looking price, you’ll end up with one hell of a result.