Using Large cover or concealment
The cognitive dissonance you are experiencing is addressed in the rules. In order to attempt to stealth, you need to not be Observed.
Being Observed If people are observing you using any of their senses (but typically sight), you can’t use Stealth. Against most creatures, finding cover or concealment allows you to use Stealth.
Cover is much harder to come by for Large creatures. Where a Medium creature may be able to find a single tree to provide Cover, a Large creature would need at least a few to prevent lines of sight to its 4x4's corners. These difficulties increase (as does the Size Penalty on Stealth) as you look at larger creatures.
Concealment can be a little easier to come by (a heavy fog is enough to do it) and a person or creature using fog/smoke/etc. to strike its foes unaware is a fairly frequent trope in media.
It may help to remember that Large represents creatures between slightly larger than large humans to creatures about 4x our size. Even massive men can be rather stealthy, and a Large creature putting in the same effort can be nearly as much so given the correct environment.