When there is tension, or even Conflict this can cause undesirable behaviour, such as irritability, stress and anger. To be effective and productive, assume positive intent. While Expectations are premeditated resentments, assuming a negative intent means building up expectations of an interaction and having to second-guess motivations.
This doesn't mean that you can't be skeptical, trust is still an important factor. However, this is more common in low-trust environments, so work to Building high-trust environments by assuming positive intent, until that trust is violated.