Even really badass designers make poor calls. We sometimes design things that can’t work or don’t make sense to users. We have personal pet preferences and theories. We make assumptions based on our prior experience, or what we’d like to be true.
We combat this with data. You can start with good data by doing research before drawing your flows and wireframes. You can test your assumptions by showing in progress work to potential users. You can test competing options with A/B tests. You can test your flows watching traffic once the design is live.
What we can’t do is expect everyone to trust us because we’re experts. We make mistakes just like everyone else. No matter how sure or confident we feel, if we’re not going out to get data and validate our opinion it’s just that; a big fat untested opinion.