You'll think a tool you built is easier to use than it is

For a tool to be easy to use, it has to be similar to priors that you already have.

Navigating novelty requires good priors to use as a foundation of understanding for that last leap of novelty.

Without the right priors the novelty might be overwhelming and lead someone to give up.

When you make the tool, your priors include precisely how it works, because you made the tool.

Whereas the priors of your users will be different and less fleshed out for that specific need than yours is from creating it.