Every single job posting doesn't take a person's full humanity into account in it's description. Society's expectations of mothers do not take their full humanity into account. Each person we know just knows us from their vantage point, they do not know all of our fears, insecurities, dreams, etc. The reality is that no one will fully know us 100%, not even ourselves. In a world full of categories and titles, we fit perfectly into none of them because we are beyond measure, beyond being fully 100% understood. So no wonder we feel like imposters because, in many ways, we are.
To fit into the role of dutiful mother, we must separate from the parts of ourselves that dislike motherhood or would rather be doing something else. To fit the role of a good worker, we deny our basic needs or force ourselves to smile during meetings that we actually despise. We don't live up to everyone's idea of us and we become worried. Worried that one day, they are going to find out that we haven't read enough books or that we don't really know how to do everything written in our job description or that we've been faking it all along. One day, they will know that we've yelled at our kids before and we will lose the title of perfect "good mom".
Most of us feel like imposters because we have not fully accepted ourselves for who we are. Instead, we keep trying to force ourselves to fit into boxes in order to achieve outside approval. We desperately believe that with enough outside approval we will finally approve of ourselves. We will finally be good enough. We are terrified to find out we've been imperfect all along and that we'll never fit into those boxes. Once we let go of the struggle of fitting into boxes such as "good mothers", "experts", etc the sooner we can begin to live a life that feels authentic and real.
You are a work in progress and that's ok. You are good enough exactly as you are. The point of life is not to achieve some static level of perfection. The point of life is to be alive. To be alive is to be imperfect. At the end of the day, there is no perfect person who has the capability to judge if you did things right or not anyway. Everyone who judges you now is imperfect themselves. What truly matters is if you are living your life fully and taking time to examine your life in order to live it well.