The fact is that these assumptions and hopes keep us going forward. However, we should be aware that these are mere assumptions. When we do not clearly label our assumptions, they become our expectations. When expectations are not met, we get disappointed.
So, never go too far. In any project, clearly document your assumptions. They may or may not be valid. You may want to validate them. If you do not document, you would not be able to take any explicit interrogation.
Hence, assumptions and hopes keep us going forward, but you should be aware of them!