We all make assumptions.  It is absolutely necessary to do so.  Our lives would be unbearably complicated if we couldn't.  If we had to assume that we knew nothing about how people we knew behaved or what to expect from them in certain circumstances.  On the other hand, assumptions can be wrong and we may never realize it.
    Recently, on several occasions, I scolded by dog Cocoa for taking his toys outside and leaving them outdoors in the rain.  Than I saw my other dog, Nova, come in the house, grab one of the toys, and carry it outside.  I had assumed it was Cocoa because he is the one who mostly plays with the toys and I rarely see Nova with a toy after the first day I buy them.  It never dawned on me that Nova might be the one taking the toys outside where she could play without interference from Cocoa because Nova is an outdoor dog and Cocoa is an indoor dog.
    So it's fine to make assumptions with things that are nearly certain, like the sun will rise in the morning, but when it come to people and pets, we need to remember that change is always possible so we need to allow for change even while we make assumptions.  Like the weather man who says 50% chance of rain, or 70%, or even 90%, but almost never 100%, because things, and people,  can catch us by surprise, no matter how well we think we know them.