One thing I've come to realize is that making assumptions is the source of conflict, misalignment, and falsehoods. The better approach is to live your life without making assumptions.
When leading a team, don't assume your mission and plan are clear; instead, make them explicit and remove any guesswork about whether everyone understands them as you do. Assuming that something is obvious risks gradual misalignment hurting your progress and culture.
In honest conversations with those around you, assuming that your critical feedback was clear enough is dangerous. To provoke real change, you need to be explicit and ensure the other person deeply understands the point you're making. Assuming they got it sets you up for conflict.
When building a company, assuming you already know the ground truth can lead you off track from creating something meaningful that actually works. Your primary job is to replace your assumptions with facts, even when it's uncomfortable. Great things can only be built from a truthful representation of the world—facts, not assumptions and theories.
To be effective in anything you do, don't make assumptions. Clarify. Repeat. Communicate. Be curious and exchange assumptions for facts.