It is easy to articulate your purpose for small actions because Individual actions use fewer knowlege. It is difficult to articulate your purpose for an entire life because life is a project and Projects require more complex information than individual actions. Accumulating necessary information this takes time. You need to find your purpose through divergence–convergence, which could take years.
To make things more challenging, none of the things that you articulate as the purpose for your small actions or even projects, could ever explain the point of your life as a whole.
References
Nagel, T. (1987). What Does It All Mean? A Very Short Introduction to Philosophy (1st ed.). Oxford University Press.