Sorry, I realise I probably worded that confusingly.

If you're open to the possibility that things might not be how you assume they are, then you are not assuming they are a particular way.

But also, not all beliefs are based purely on assumptions. The most intelligent beliefs are based on observations and repeated testing. For example, my belief that gravity exists is not merely an assumption. It is based on the repeated observation that whenever I jump in the air I fall back down again.

Of course, we cannot be sure that the rules that apply on Earth apply everywhere in the universe. We also can't be sure that they don't. So, when faced with a lack of evidence either way, it's not unintelligent to assume they do.