Dissatisfying take: It's both true and untrue.

Your mindset absolutely has an influence on outcomes - how you come off to other people influences how they react to you and treat you. How you look at a problem influences whether you decide to engage with it, and how.

This exists in a gradient space - some things are more readily influenced in this way, others are not, a few are (nearly) completely untouched.

Existence, that is - the Universe, is a complex system. We know at least a few things about those:

- they behave in unintuitive ways. Attempting to predict the behavior of a complex system has an inverse relationship with the granularity and specificity of the prediction.

- the behavior of the whole is unrepresentable in the behavior of the constituent parts (you cannot drive an axle to work, unless it is part of a car)

- they are very resilient against attempts at control, but more susceptible to influence

- they can exhibit features like recursion, inertia, and attraction. Each of these has specific consequences for the behavior of the whole.

The relationship between outlook and outcome is bidirectional - one influences the other and vice versa. This structure has a high chance to exhibit recursive reinforcement, which is why I think we're used to seeing very optimistic and very pessimistic outlooks, with not so many 'middle-of-the-road' types. It does provide a lever to push, however, if one has the fortitude to push through the failures on the way to that tipping point.