At the same time we are very certain on some issues.

As an example there will not be a theory which says "You can lift yourself up" and suddenly people grabbing their own belts could lift themselves up into the air.

Any future theory will predict exactly the same things as current theories on the cases where current theories have been experimentally verified.

Whatever we find out has to reduce to what we know now in the conditions we've already looked at. That contrains what we will discover in the future.