That's how all compressors work, in that likely files (eg. ASCII, obvious patterns, etc) become smaller and unlikely files become bigger.

Right, but the point was, the case where it became bigger was ~impossible to find.

> likely files (eg. ASCII, obvious patterns, etc) become smaller

Likely files for a real human workload are like that, but if "most inputs" is talking about the set of all possible files, then that's a whole different ball game and "most inputs" will compress very badly.

> unlikely files become bigger

Yes, but when compressors can't find useful patterns they generally only increase size by a small fraction of a percent. There aren't files that get significantly bigger.

In some cases it can be certain, the ascii encoded in the usual 8 bits has fat to trim even if it is random in that space.